MySQL Tutorial
MySQL is the most popular Open Source Relational SQL database management system. MySQL is one of the best RDBMS being used for developing web based software applications.
MySQL Introduction
What is Database?
A database is a separate application that stores a collection of data. Each database has one or more distinct APIs for creating, accessing, managing, searching, and replicating the data it holds.
Other kinds of data stores can be used, such as files on the file system or large hash tables in memory but data fetching and writing would not be so fast and easy with those type of systems.
So now a days we use relational database management systems (RDBMS) to store and manager huge volume of data. This is called relational database because all the data is stored into different tables and relations are established using primary keys or other keys known as foreign keys.
A Relational DataBase Management System (RDBMS) is a software that:
- Enables you to implement a database with tables, columns, and indexes.
- Guarantees the Referential Integrity between rows of various tables.
- Updates the indexes automatically.
- Interprets an SQL query and combines information from various tables.
RDBMS Terminology:
Before we proceed to explain MySQL database system, lets revise few definitions related to database.
- Database: A database is a collection of tables, with related data.
- Table: A table is a matrix with data. A table in a database looks like a simple spreadsheet.
- Column: One column (data element) contains data of one and the same kind, for example the column postcode.
- Row: A row (= tuple, entry or record) is a group of related data, for example the data of one subscription.
- Redundancy: Storing data twice, redundantly to make the system faster.
- Primary Key: A primary key is unique. A key value can not occur twice in one table. With a key you can find at most one row.
- Foreign Key: A foreign key is the linking pin between two tables.
- Compound Key: A compound key (composite key) is a key that consists of multiple columns, because one column is not sufficiently unique.
- Index: An index in a database resembles an index at the back of a book.
- Referential Integrity: Referential Integrity makes sure that a foreign key value always points to an existing row.
MySQL Database:
MySQL is a fast, easy-to-use RDBMS used being used for many small and big businesses. MySQL is developed, marketed, and supported by MySQL AB, which is a Swedish company. MySQL is becoming so popular because of many good reasons.
- MySQL is released under an open-source license. So you have nothing to pay to use it.
- MySQL is a very powerful program in its own right. It handles a large subset of the functionality of the most expensive and powerful database packages.
- MySQL uses a standard form of the well-known SQL data language.
- MySQL works on many operating systems and with many languages including PHP, PERL, C, C++, JAVA etc.
- MySQL works very quickly and works well even with large data sets.
- MySQL is very friendly to PHP, the most appreciated language for web development.
- MySQL supports large databases, up to 50 million rows or more in a table. The default file size limit for a table is 4GB, but you can increase this (if your operating system can handle it) to a theoretical limit of 8 million terabytes (TB).
- MySQL is customizable. The open source GPL license allows programmers to modify the MySQL software to fit their own specific environments.
Before You Begin:
Before you begin this tutorial you should have a basic knowledge of the information covered in our PHP and HTML tutorials.
This tutorial focuses heavily on using MySQL in a PHP environment. Many examples given in this tutorial will be useful for PHP Programmers.
MySQL Installation - Linux and Windows
Downloading MySQL:
All downloads for MySQL are located at MySQL Downloads. Pick the version number for MySQL Community Server you want and, as exactly as possible, the platform you want.
Installing MySQL on Linux/Unix
The recommended way to install MySQL on a Linux system is via RPM. MySQL AB makes the following RPMs available for download on its web site:
- MySQL - The MySQL database server, which manages databases and tables, controls user access, and processes SQL queries.
- MySQL-client - MySQL client programs, which makes it possible to connect to, and interact with, the server.
- MySQL-devel - Libraries and header files that come in handy when compiling other programs that use MySQL.
- MySQL-shared - Shared libraries for the MySQL client
- MySQL-bench - Benchmark and performance testing tools for the MySQL database server.
The MySQL RPMs listed here are all built on a SuSE Linux system, but they.ll usually work on other Linux variants with no difficulty.
Now follow the following steps to proceed for installation:
- Login to the system using root user.
- Switch to the directory containing the RPMs:
- Install the MySQL database server by executing the following command. Remember to replace the filename in italics with the file name of your RPM.
[root@host]# rpm -i MySQL-5.0.9-0.i386.rpm
Above command takes care of installing MySQL server, creating a user of MySQL, creating necessary configuration and starting MySQL server automatically.You can find all the MySQL related binaries in /usr/bin and /usr/sbin. All the tables and databases will be created in /var/lib/mysql directory. - This is optional but recommended step to install the remaining RPMs in the same manner:
[root@host]# rpm -i MySQL-client-5.0.9-0.i386.rpm [root@host]# rpm -i MySQL-devel-5.0.9-0.i386.rpm [root@host]# rpm -i MySQL-shared-5.0.9-0.i386.rpm [root@host]# rpm -i MySQL-bench-5.0.9-0.i386.rpm
Installing MySQL on Windows:
Default installation on any version of Windows is now much easier than it used to be, as MySQL now comes neatly packaged with an installer. Simply download the installer package, unzip it anywhere, and run setup.exe.
Default installer setup.exe will walk you through the trivial process and by default will install everything under C:\mysql.
Test the server by firing it up from the command prompt the first time. Go to the location of the mysqld server, which is probably C:\mysql\bin, and type:
mysqld.exe --console
NOTE: If you are on NT then you will have to use mysqld-nt.exe instead of mysqld.exe
If all went well, you will see some messages about startup and InnoDB. If not, you may have a permissions issue. Make sure that the directory that holds your data is accessible to whatever user (probably mysql) the database processes run under.
MySQL will not add itself to the start menu, and there is no particularly nice GUI way to stop the server either. Therefore, if you tend to start the server by double clicking the mysqld executable, you should remember to halt the process by hand by using mysqladmin, Task List, Task Manager, or other Windows-specific means.
Verifying MySQL Installation:
After MySQL has been successfully installed, the base tables have been initialized, and the server has been started, you can verify that all is working as it should via some simple tests.
Use the mysqladmin Utility to Obtain Server Status:
Use mysqladmin binary to check server version. This binary would be available in /usr/bin on linux and in C:\mysql\bin on windows.
[root@host]# mysqladmin --version
It will produce following result on Linux. It may vary depending on your installation:
mysqladmin Ver 8.23 Distrib 5.0.9-0, for redhat-linux-gnu on i386
If you do not get such message then there may be some problem in your installation and you would need some help to fix it.
Execute simple SQL commands using MySQL Client:
You can connect to your MySQL server by using MySQL client using mysql command. At this momemnt you do not need to give any password as by default it will be set to blank.
So just use following command
[root@host]# mysql
It should be rewarded with a mysql> prompt. Now you are connected to the MySQL server and you can execute all the SQL command at mysql> prompt as follows.
mysql> SHOW DATABASES; +----------+ | Database | +----------+ | mysql | | test | +----------+ 2 rows in set (0.13 sec)
Post-installation Steps:
MySQL ships with a blank password for the root MySQL user. As soon as you have successfully installed the database and client you need to set a root password as follows:
[root@host]# mysqladmin -u root password "new_password";
Now to make a connection to your MySQL server you would have to use following command:
[root@host]# mysql -u root -p Enter password:*******
Unix users will also want to put your MySQL directory in your PATH, so you won't have to keep typing out the full path every time you want to use the command-line client. For bash, it would be something like:
export PATH=$PATH:/usr/bin:/usr/sbin
Running MySQL at boot time:
If you want to run MySQL server at boot time then make sure you have following entry in /etc/rc.local file
/etc/init.d/mysqld start
Also,you should have mysqld binary in /etc/init.d/ directory.
MySQL Administration
Running and Shutting down MySQL Server:
First check if your MySQL server is running or not. You can use following command to check this:
ps -ef | grep mysqld
If your MySql is running then you will see mysqld process listed out in your result. If server is not running then you can start it by using following command:
root@host# cd /usr/bin ./safe_mysqld &
Now if you want to shutdown an already running MySQL server then you can do it by using following command:
root@host# cd /usr/bin ./mysqladmin -u root -p shutdown Enter password: ******
Setting Up a MySQL User Accounts:
For adding a new user to MySQL you just need to add a new entry to user table in database mysql.
Below is an example of adding new user guest with SELECT, INSERT and UPDATE privileges with the password guest123 the SQL query is :
root@host# mysql -u root -p Enter password:******* mysql> use mysql; Database changed mysql> INSERT INTO user (host, user, password, select_priv, insert_priv, update_priv) VALUES ('localhost', 'guest', PASSWORD('guest123'), 'Y', 'Y', 'Y'); Query OK, 1 row affected (0.20 sec) mysql> FLUSH PRIVILEGES; Query OK, 1 row affected (0.01 sec) mysql> SELECT host, user, password FROM user WHERE user = 'guest'; +-----------+---------+------------------+ | host | user | password | +-----------+---------+------------------+ | localhost | guest | 6f8c114b58f2ce9e | +-----------+---------+------------------+ 1 row in set (0.00 sec)
When adding a new user remember to encrypt the new password using PASSWORD() function provided by MySQL. As you can see in the above example the password mypass is encrypted to 6f8c114b58f2ce9e.
Notice the FLUSH PRIVILEGES statement. This tells the server to reload the grant tables. If you don't use it then you won't be able to connect to mysql using the new user account at least until the server is rebooted.
You can also specify other privileges to a new user by setting the values of following columns in user table to 'Y' when executing the INSERT query or you can update them later using UPDATE query.
- Select_priv
- Insert_priv
- Update_priv
- Delete_priv
- Create_priv
- Drop_priv
- Reload_priv
- Shutdown_priv
- Process_priv
- File_priv
- Grant_priv
- References_priv
- Index_priv
- Alter_priv
Another way of adding user account is by using GRANT SQL command; Following example will ada user zara with password zara123 for a particular database called TUTORIALS.
root@host# mysql -u root -p password; Enter password:******* mysql> use mysql; Database changed mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP -> ON TUTORIALS.* -> TO 'zara'@'localhost' -> IDENTIFIED BY 'zara123';
This will also create an entry in mysql database table called user.
NOTE: MySQL does not terminate a command until you give a semi colon (;) at the end of SQL command.
The /etc/my.cnf File Configuration:
Most of the cases you should not touch this file. By default it will have following entries:
[mysqld] datadir=/var/lib/mysql socket=/var/lib/mysql/mysql.sock [mysql.server] user=mysql basedir=/var/lib [safe_mysqld] err-log=/var/log/mysqld.log pid-file=/var/run/mysqld/mysqld.pid
Here you can specify a different directory for error log, otherwise you should not change any entry in this table.
Administrative MySQL Command:
Here is the list of important MySQL command which you will use time to time to work with MySQL database:
- USE Databasename : This will be used to select a particular database in MySQL workarea.
- SHOW DATABASES: Lists the databases that are accessible by the MySQL DBMS.
- SHOW TABLES: Shows the tables in the database once a database has been selected with the use command.
- SHOW COLUMNS FROM tablename: Shows the attributes, types of attributes, key information, whether NULL is permitted, defaults, and other information for a table.
- SHOW INDEX FROM tablename: Presents the details of all indexes on the table, including the PRIMARY KEY.
- SHOW TABLE STATUS LIKE tablename\G: Reports details of the MySQL DBMS performance and statistics.
MySQL PHP Syntax
MySQL works very well in combination of various programming languages like PERL, C, C++, JAVA and PHP. Out of these languages, PHP is the most popular one because of its web application development capabilities.
PHP provides various functions to access MySQL database and to manipulate data records inside MySQL database. You would require to call PHP functions in the same way you call any other PHP function.
The PHP functions for use with MySQL have the following general format:
mysql_function(value,value,...);
The second part of the function name is specific to the function, usually a word that describes what the function does. The following are two of the functions which we will use in our tutorial
mysqli_connect($connect); mysqli_query($connect,"SQL statement");
Following example shows a generic sysntax of PHP to call any MySQL function.
<html> <head> <title>PHP with MySQL</title> </head> <body> <?php $retval = mysql_function(value, [value,...]); if( !$retval ) { die ( "Error: a related error message" ); } // Otherwise MySQL or PHP Statements ?> </body> </html>
MySQL Connection
MySQL Connection using mysql binary:
You can establish MySQL database using mysql binary at command prompt.
Example:
Here is a simple example to connect to MySQL server from command prompt:
[root@host]# mysql -u root -p Enter password:******
This will give you mysql> command prompt where you will be able to execute any SQL command. Following is the result of above command:
Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 2854760 to server version: 5.0.9 Type 'help;' or '\h' for help. Type '\c' to clear the buffer.
In above example we have used root as a user but you can use any other user. Any user will be able to perform all the SQL operation which are allowed to that user.
You can disconnect from MySQL database any time using exit command at mysql> prompt.
mysql> exit Bye
MySQL Connection using PHP Script:
PHP provides mysql_connect() function to open a database connection. This function takes five parameters and returns a MySQL link identifier on success, or FALSE on failure.
Syntax:
connection mysql_connect(server,user,passwd,new_link,client_flag);
| Parameter | Description |
|---|---|
| server | Optional - The host name running database server. If not specified then default value is localhost:3036. |
| user | Optional - The username accessing the database. If not specified then default is the name of the user that owns the server process. |
| passwd | Optional - The password of the user accessing the database. If not specified then default is an empty password. |
| new_link | Optional - If a second call is made to mysql_connect() with the same arguments, no new connection will be established; instead, the identifier of the already opened connection will be returned. |
| client_flags | Optional - A combination of the following constants:
|
You can disconnect from MySQL database anytime using another PHP function mysql_close(). This function takes a single parameter which is a connection returned by mysql_connect() function.
Syntax:
bool mysql_close ( resource $link_identifier );
If a resource is not specified then last opened database is closed. This function returns true if it closes connection successfully otherwise it returns false.
Example:
Try out following example to connect to a MySQL server:
<html> <head> <title>Connecting MySQL Server</title> </head> <body> <?php $dbhost = 'localhost:3036'; $dbuser = 'guest'; $dbpass = 'guest123'; $conn = mysql_connect($dbhost, $dbuser, $dbpass); if(! $conn ) { die('Could not connect: ' . mysql_error()); } echo 'Connected successfully'; mysql_close($conn); ?> </body> </html>
Create MySQL Database
Create Database using mysqladmin:
You would need special privilege to create or to delete a MySQL database. So assuming you have access to root user, you can create any database using mysql mysqladmin binary.
Example:
Here is a simple example to create database called TUTORIALS:
[root@host]# mysqladmin -u root -p create TUTORIALS Enter password:******
This will create a MySQL database TUTORIALS.
Create Database using PHP Script:
PHP uses mysql_query function to create or delete a MySQL database. This function takes two parameters and returns TRUE on success or FALSE on failure.
Syntax:
bool mysql_query( sql, connection );
| Parameter | Description |
|---|---|
| sql | Required - SQL query to create or delete a MySQL database |
| connection | Optional - if not specified then last opened connection by mysql_connect will be used. |
Example:
Try out following example to create a database:
<html> <head> <title>Creating MySQL Database</title> </head> <body> <?php $dbhost = 'localhost:3036'; $dbuser = 'root'; $dbpass = 'rootpassword'; $conn = mysql_connect($dbhost, $dbuser, $dbpass); if(! $conn ) { die('Could not connect: ' . mysql_error()); } echo 'Connected successfully<br />'; $sql = 'CREATE DATABASE TUTORIALS'; $retval = mysql_query( $sql, $conn ); if(! $retval ) { die('Could not create database: ' . mysql_error()); } echo "Database TUTORIALS created successfully\n"; mysql_close($conn); ?> </body> </html>
Drop MySQL Database
Drop Database using mysqladmin:
You would need special privilege to create or to delete a MySQL database. So assuming you have access to root user, you can create any database using mysql mysqladmin binary.
Be careful while deleting any database because it will lose your all the data available in your database.
Here is an example to delete a database created in previous chapter:
[root@host]# mysqladmin -u root -p drop TUTORIALS Enter password:******
This will give you a warning and it will confirm if you really want to delete this database or not.
Dropping the database is potentially a very bad thing to do. Any data stored in the database will be destroyed. Do you really want to drop the 'TUTORIALS' database [y/N] y Database "TUTORIALS" dropped
Drop Database using PHP Script:
PHP uses mysql_query function to create or delete a MySQL database. This function takes two parameters and returns TRUE on success or FALSE on failure.
Syntax:
bool mysql_query( sql, connection );
| Parameter | Description |
|---|---|
| sql | Required - SQL query to create or delete a MySQL database |
| connection | Optional - if not specified then last opened connection by mysql_connect will be used. |
Example:
Try out following example to delete a database:
<html> <head> <title>Deleting MySQL Database</title> </head> <body> <?php $dbhost = 'localhost:3036'; $dbuser = 'root'; $dbpass = 'rootpassword'; $conn = mysql_connect($dbhost, $dbuser, $dbpass); if(! $conn ) { die('Could not connect: ' . mysql_error()); } echo 'Connected successfully<br />'; $sql = 'DROP DATABASE TUTORIALS'; $retval = mysql_query( $sql, $conn ); if(! $retval ) { die('Could not delete database: ' . mysql_error()); } echo "Database TUTORIALS deleted successfully\n"; mysql_close($conn); ?> </body> </html>
WARNING: While deleting a database using PHP script, it does not prompt you for any confirmation. So be careful while deleting a MySQL database.
Selecting MySQL Database
Once you get connection with MySQL server,it is required to select a particular database to work with. This is because there may be more than one database available with MySQL Server.
Selecting MySQL Database from Command Prompt:
This is very simple to select a particular database from mysql> prompt. You can use SQL commanduse to select a particular database.
Example:
Here is an example to select database called TUTORIALS:
[root@host]# mysql -u root -p Enter password:****** mysql> use TUTORIALS; Database changed mysql>
Now you have selected TUTORIALS database and all the subsequent operations will be performed on TUTORIALS database.
NOTE: all the database name, table names, table fields name are case sensitive. So you would have to use prpoer names while giving any SQL command.
Selecting MySQL Database Using PHP Script:
PHP provides function mysql_select_db to select a database.It returns TRUE on success or FALSE on failure.
Syntax:
bool mysql_select_db( db_name, connection );
| Parameter | Description |
|---|---|
| db_name | Required - MySQL Database name to be selected |
| connection | Optional - if not specified then last opened connection by mysql_connect will be used. |
Example:
Here is the example showing you how to select a database.
<html> <head> <title>Selecting MySQL Database</title> </head> <body> <?php $dbhost = 'localhost:3036'; $dbuser = 'guest'; $dbpass = 'guest123'; $conn = mysql_connect($dbhost, $dbuser, $dbpass); if(! $conn ) { die('Could not connect: ' . mysql_error()); } echo 'Connected successfully'; mysql_select_db( 'TUTORIALS' ); mysql_close($conn); ?> </body> </html>
MySQL Data Types
Properly defining the fields in a table is important to the overall optimization of your database. You should use only the type and size of field you really need to use; don't define a field as 10 characters wide if you know you're only going to use 2 characters. These types of fields (or columns) are also referred to as data types, after the type of data you will be storing in those fields.
MySQL uses many different data types, broken into three categories: numeric, date and time, and string types.
Numeric Data Types:
MySQL uses all the standard ANSI SQL numeric data types, so if you're coming to MySQL from a different database system, these definitions will look familiar to you. The following list shows the common numeric data types and their descriptions.
- INT - A normal-sized integer that can be signed or unsigned. If signed, the allowable range is from -2147483648 to 2147483647. If unsigned, the allowable range is from 0 to 4294967295. You can specify a width of up to 11 digits.
- TINYINT - A very small integer that can be signed or unsigned. If signed, the allowable range is from -128 to 127. If unsigned, the allowable range is from 0 to 255. You can specify a width of up to 4 digits.
- SMALLINT - A small integer that can be signed or unsigned. If signed, the allowable range is from -32768 to 32767. If unsigned, the allowable range is from 0 to 65535. You can specify a width of up to 5 digits.
- MEDIUMINT - A medium-sized integer that can be signed or unsigned. If signed, the allowable range is from -8388608 to 8388607. If unsigned, the allowable range is from 0 to 16777215. You can specify a width of up to 9 digits.
- BIGINT - A large integer that can be signed or unsigned. If signed, the allowable range is from -9223372036854775808 to 9223372036854775807. If unsigned, the allowable range is from 0 to 18446744073709551615. You can specify a width of up to 11 digits.
- FLOAT(M,D) - A floating-point number that cannot be unsigned. You can define the display length (M) and the number of decimals (D). This is not required and will default to 10,2, where 2 is the number of decimals and 10 is the total number of digits (including decimals). Decimal precision can go to 24 places for a FLOAT.
- DOUBLE(M,D) - A double precision floating-point number that cannot be unsigned. You can define the display length (M) and the number of decimals (D). This is not required and will default to 16,4, where 4 is the number of decimals. Decimal precision can go to 53 places for a DOUBLE. REAL is a synonym for DOUBLE.
- DECIMAL(M,D) - An unpacked floating-point number that cannot be unsigned. In unpacked decimals, each decimal corresponds to one byte. Defining the display length (M) and the number of decimals (D) is required. NUMERIC is a synonym for DECIMAL.
Date and Time Types:
The MySQL date and time datatypes are:
- DATE - A date in YYYY-MM-DD format, between 1000-01-01 and 9999-12-31. For example, December 30th, 1973 would be stored as 1973-12-30.
- DATETIME - A date and time combination in YYYY-MM-DD HH:MM:SS format, between 1000-01-01 00:00:00 and 9999-12-31 23:59:59. For example, 3:30 in the afternoon on December 30th, 1973 would be stored as 1973-12-30 15:30:00.
- TIMESTAMP - A timestamp between midnight, January 1, 1970 and sometime in 2037. This looks like the previous DATETIME format, only without the hyphens between numbers; 3:30 in the afternoon on December 30th, 1973 would be stored as 19731230153000 ( YYYYMMDDHHMMSS ).
- TIME - Stores the time in HH:MM:SS format.
- YEAR(M) - Stores a year in 2-digit or 4-digit format. If the length is specified as 2 (for example YEAR(2)), YEAR can be 1970 to 2069 (70 to 69). If the length is specified as 4, YEAR can be 1901 to 2155. The default length is 4.
String Types:
Although numeric and date types are fun, most data you'll store will be in string format. This list describes the common string datatypes in MySQL.
- CHAR(M) - A fixed-length string between 1 and 255 characters in length (for example CHAR(5)), right-padded with spaces to the specified length when stored. Defining a length is not required, but the default is 1.
- VARCHAR(M) - A variable-length string between 1 and 255 characters in length; for example VARCHAR(25). You must define a length when creating a VARCHAR field.
- BLOB or TEXT - A field with a maximum length of 65535 characters. BLOBs are "Binary Large Objects" and are used to store large amounts of binary data, such as images or other types of files. Fields defined as TEXT also hold large amounts of data; the difference between the two is that sorts and comparisons on stored data are case sensitive on BLOBs and are not case sensitive in TEXT fields. You do not specify a length with BLOB or TEXT.
- TINYBLOB or TINYTEXT - A BLOB or TEXT column with a maximum length of 255 characters. You do not specify a length with TINYBLOB or TINYTEXT.
- MEDIUMBLOB or MEDIUMTEXT - A BLOB or TEXT column with a maximum length of 16777215 characters. You do not specify a length with MEDIUMBLOB or MEDIUMTEXT.
- LONGBLOB or LONGTEXT - A BLOB or TEXT column with a maximum length of 4294967295 characters. You do not specify a length with LONGBLOB or LONGTEXT.
- ENUM - An enumeration, which is a fancy term for list. When defining an ENUM, you are creating a list of items from which the value must be selected (or it can be NULL). For example, if you wanted your field to contain "A" or "B" or "C", you would define your ENUM as ENUM ('A', 'B', 'C') and only those values (or NULL) could ever populate that field.
Create MySQL Tables
The table creation command requires:
- Name of the table
- Names of fields
- Definitions for each field
Syntax:
Here is generic SQL syntax to create a MySQL table:
CREATE TABLE table_name (column_name column_type);
Now we will create following table in TUTORIALS database.
tutorials_tbl( tutorial_id INT NOT NULL AUTO_INCREMENT, tutorial_title VARCHAR(100) NOT NULL, tutorial_author VARCHAR(40) NOT NULL, submission_date DATE, PRIMARY KEY ( tutorial_id ) );
Here few items need explanation:
- Field Attribute NOT NULL is being used because we do not want this field to be NULL. SO if user will try to create a record with NULL value then MySQL will raise an error.
- Field Attribute AUTO_INCREMENT tells to MySQL to go ahead and add the next available number to the id field.
- Keyword PRIMARY KEY is used to define a column as primary key. You can use multiple columns separated by comma to define a primary key.
Creating Tables from Command Prompt:
This is easy to create a MySQL table from mysql> prompt. You will use SQL command CREATE TABLEto create a table.
Example:
Here is an example which creates tutorials_tbl:
root@host# mysql -u root -p Enter password:******* mysql> use TUTORIALS; Database changed mysql> CREATE TABLE tutorials_tbl( -> tutorial_id INT NOT NULL AUTO_INCREMENT, -> tutorial_title VARCHAR(100) NOT NULL, -> tutorial_author VARCHAR(40) NOT NULL, -> submission_date DATE, -> PRIMARY KEY ( tutorial_id ) -> ); Query OK, 0 rows affected (0.16 sec) mysql>
NOTE: MySQL does not terminate a command until you give a semi colon (;) at the end of SQL command.
Creating Tables Using PHP Script:
To create new table in any existing database you would need to use PHP function mysql_query(). You will pass its second argument with proper SQL command to create a table.
Example:
Here is an example to create a table using PHP script:
<html> <head> <title>Creating MySQL Tables</title> </head> <body> <?php $dbhost = 'localhost:3036'; $dbuser = 'root'; $dbpass = 'rootpassword'; $conn = mysql_connect($dbhost, $dbuser, $dbpass); if(! $conn ) { die('Could not connect: ' . mysql_error()); } echo 'Connected successfully<br />'; $sql = "CREATE TABLE tutorials_tbl( ". "tutorial_id INT NOT NULL AUTO_INCREMENT, ". "tutorial_title VARCHAR(100) NOT NULL, ". "tutorial_author VARCHAR(40) NOT NULL, ". "submission_date DATE, ". "PRIMARY KEY ( tutorial_id )); "; mysql_select_db( 'TUTORIALS' ); $retval = mysql_query( $sql, $conn ); if(! $retval ) { die('Could not create table: ' . mysql_error()); } echo "Table created successfully\n"; mysql_close($conn); ?> </body> </html>
Drop MySQL Tables
It is very easy to drop an existing MySQL table. But you need to be very careful while deleting any existing table because data lost will not be recovered after deleting a table.
Syntax:
Here is generic SQL syntax to drop a MySQL table:
DROP TABLE table_name ;
Dropping Tables from Command Prompt:
This needs just to execute DROP TABLE SQL command at mysql> prompt.
Example:
Here is an example which deletes tutorials_tbl:
root@host# mysql -u root -p Enter password:******* mysql> use TUTORIALS; Database changed mysql> DROP TABLE tutorials_tbl Query OK, 0 rows affected (0.8 sec) mysql>
Dropping Tables Using PHP Script:
To drop an existing table in any database you would need to use PHP function mysql_query(). You will pass its second argument with proper SQL command to drop a table.
Example:
<html> <head> <title>Creating MySQL Tables</title> </head> <body> <?php $dbhost = 'localhost:3036'; $dbuser = 'root'; $dbpass = 'rootpassword'; $conn = mysql_connect($dbhost, $dbuser, $dbpass); if(! $conn ) { die('Could not connect: ' . mysql_error()); } echo 'Connected successfully<br />'; $sql = "DROP TABLE tutorials_tbl"; mysql_select_db( 'TUTORIALS' ); $retval = mysql_query( $sql, $conn ); if(! $retval ) { die('Could not delete table: ' . mysql_error()); } echo "Table deleted successfully\n"; mysql_close($conn); ?> </body> </html>
MySQL INSERT Query
To insert data into MySQL table you would need to use SQL INSERT INTO command. You can insert data into MySQL table by using mysql> prompt or by using any script like PHP.
Syntax:
Here is generic SQL syntax of INSERT INTO command to insert data into MySQL table:
INSERT INTO table_name ( field1, field2,...fieldN ) VALUES ( value1, value2,...valueN );
To insert string data types it is required to keep all the values into double or single quote, for example:-"value".
Inserting Data from Command Prompt:
This will use SQL INSERT INTO command to insert data into MySQL table tutorials_tbl
Example:
Following example will create 3 records into tutorials_tbl table:
root@host# mysql -u root -p password; Enter password:******* mysql> use TUTORIALS; Database changed mysql> INSERT INTO tutorials_tbl ->(tutorial_title, tutorial_author, submission_date) ->VALUES ->("Learn PHP", "John Poul", NOW()); Query OK, 1 row affected (0.01 sec) mysql> INSERT INTO tutorials_tbl ->(tutorial_title, tutorial_author, submission_date) ->VALUES ->("Learn MySQL", "Abdul S", NOW()); Query OK, 1 row affected (0.01 sec) mysql> INSERT INTO tutorials_tbl ->(tutorial_title, tutorial_author, submission_date) ->VALUES ->("JAVA Tutorial", "Sanjay", '2007-05-06'); Query OK, 1 row affected (0.01 sec) mysql>
NOTE: Please note that all the arrow signs (->) are not part of SQL command they are indicating a new line and they are created automatically by MySQL prompt while pressing enter key without giving a semi colon at the end of each line of the command.
In the above example we have not provided tutorial_id because at the time of table create we had given AUTO_INCREMENT option for this field. So MySQL takes care of inserting these IDs automatically. Here NOW() is a MySQL function which returns current date and time.
Inserting Data Using PHP Script:
You can use same SQL INSERT INTO command into PHP function mysql_query() to insert data into a MySQL table.
Example:
This example will take three parameters from user and will insert them into MySQL table:
<html> <head> <title>Add New Record in MySQL Database</title> </head> <body> <?php if(isset($_POST['add'])) { $dbhost = 'localhost:3036'; $dbuser = 'root'; $dbpass = 'rootpassword'; $conn = mysql_connect($dbhost, $dbuser, $dbpass); if(! $conn ) { die('Could not connect: ' . mysql_error()); } if(! get_magic_quotes_gpc() ) { $tutorial_title = addslashes ($_POST['tutorial_title']); $tutorial_author = addslashes ($_POST['tutorial_author']); } else { $tutorial_title = $_POST['tutorial_title']; $tutorial_author = $_POST['tutorial_author']; } $submission_date = $_POST['submission_date']; $sql = "INSERT INTO tutorials_tbl ". "(tutorial_title,tutorial_author, submission_date) ". "VALUES ". "('$tutorial_title','$tutorial_author','$submission_date')"; mysql_select_db('TUTORIALS'); $retval = mysql_query( $sql, $conn ); if(! $retval ) { die('Could not enter data: ' . mysql_error()); } echo "Entered data successfully\n"; mysql_close($conn); } else { ?> <form method="post" action="<?php $_PHP_SELF ?>"> <table width="600" border="0" cellspacing="1" cellpadding="2"> <tr> <td width="250">Tutorial Title</td> <td> <input name="tutorial_title" type="text" id="tutorial_title"> </td> </tr> <tr> <td width="250">Tutorial Author</td> <td> <input name="tutorial_author" type="text" id="tutorial_author"> </td> </tr> <tr> <td width="250">Submission Date [ yyyy-mm-dd ]</td> <td> <input name="submission_date" type="text" id="submission_date"> </td> </tr> <tr> <td width="250"> </td> <td> </td> </tr> <tr> <td width="250"> </td> <td> <input name="add" type="submit" id="add" value="Add Tutorial"> </td> </tr> </table> </form> <?php } ?> </body> </html>
While doing data insert its best practice to use function get_magic_quotes_gpc() to check if current configuration for magic quote is set or not. If this function returns false then use function addslashes()to add slashes before quotes.
You can put many validations around to check if entered data is correct or not and can take appropriate action.
MySQL SELECT Query
The SQL SELECT command is used to fetch data from MySQL database. You can use this command at mysql> prompt as well as in any script like PHP.
Syntax:
Here is generic SQL syntax of SELECT command to fetch data from MySQL table:
SELECT field1, field2,...fieldN table_name1, table_name2... [WHERE Clause] [OFFSET M ][LIMIT N]
- You can use one or more tables separated by comma to include various condition using a WHERE clause. But WHERE clause is an optional part of SELECT command.
- You can fetch one or more fields in a single SELECT command.
- You can specify star (*) in place of fields. In this case SELECT will return all the fields
- You can specify any condition using WHERE clause.
- You can specify an offset using OFFSET from where SELECT will start returning records. By default offset is zero
- You can limit the number of returned using LIMIT attribute.
Fetching Data from Command Prompt:
This will use SQL SELECT command to fetch data from MySQL table tutorials_tbl
Example:
Following example will return all the records from tutorials_tbl table:
root@host# mysql -u root -p password; Enter password:******* mysql> use TUTORIALS; Database changed mysql> SELECT * from tutorials_tbl +-------------+----------------+-----------------+-----------------+ | tutorial_id | tutorial_title | tutorial_author | submission_date | +-------------+----------------+-----------------+-----------------+ | 1 | Learn PHP | John Poul | 2007-05-21 | | 2 | Learn MySQL | Abdul S | 2007-05-21 | | 3 | JAVA Tutorial | Sanjay | 2007-05-21 | +-------------+----------------+-----------------+-----------------+ 3 rows in set (0.01 sec) mysql>
Fetching Data Using PHP Script:
You can use same SQL SELECT command into PHP function mysql_query(). This function is used to execute SQL command and later another PHP function mysql_fetch_array() can be used to fetch all the selected data. This function returns row as an associative array, a numeric array, or both. This function returns FALSE if there are no more rows.
Below is a simple example to fetch records from tutorials_tbl table.
Example:
Try out following example to display all the records from tutorials_tbl table.
<?php $dbhost = 'localhost:3036'; $dbuser = 'root'; $dbpass = 'rootpassword'; $conn = mysql_connect($dbhost, $dbuser, $dbpass); if(! $conn ) { die('Could not connect: ' . mysql_error()); } $sql = 'SELECT tutorial_id, tutorial_title, tutorial_author, submission_date FROM tutorials_tbl'; mysql_select_db('TUTORIALS'); $retval = mysql_query( $sql, $conn ); if(! $retval ) { die('Could not get data: ' . mysql_error()); } while($row = mysql_fetch_array($retval, MYSQL_ASSOC)) { echo "Tutorial ID :{$row['tutorial_id']} <br> ". "Title: {$row['tutorial_title']} <br> ". "Author: {$row['tutorial_author']} <br> ". "Submission Date : {$row['submission_date']} <br> ". "--------------------------------<br>"; } echo "Fetched data successfully\n"; mysql_close($conn); ?>
The content of the rows are assigned to the variable $row and the values in row are then printed.
NOTE: Always remember to put curly brackets when you want to insert an array value directly into a string.
In above example the constant MYSQL_ASSOC is used as the second argument to PHP functionmysql_fetch_array(), so that it returns the row as an associative array. With an associative array you can access the field by using their name instead of using the index.
PHP provides another function called mysql_fetch_assoc() which also returns the row as an associative array.
Example:
Try out following example to display all the records from tutorial_tbl table using mysql_fetch_assoc() function.
<?php $dbhost = 'localhost:3036'; $dbuser = 'root'; $dbpass = 'rootpassword'; $conn = mysql_connect($dbhost, $dbuser, $dbpass); if(! $conn ) { die('Could not connect: ' . mysql_error()); } $sql = 'SELECT tutorial_id, tutorial_title, tutorial_author, submission_date FROM tutorials_tbl'; mysql_select_db('TUTORIALS'); $retval = mysql_query( $sql, $conn ); if(! $retval ) { die('Could not get data: ' . mysql_error()); } while($row = mysql_fetch_assoc($retval)) { echo "Tutorial ID :{$row['tutorial_id']} <br> ". "Title: {$row['tutorial_title']} <br> ". "Author: {$row['tutorial_author']} <br> ". "Submission Date : {$row['submission_date']} <br> ". "--------------------------------<br>"; } echo "Fetched data successfully\n"; mysql_close($conn); ?>
You can also use the constant MYSQL_NUM, as the second argument to PHP function mysql_fetch_array(). This will cause the function to return an array with numeric index.
Example:
Try out following example to display all the records from tutorials_tbl table using MYSQL_NUM argument.
<?php $dbhost = 'localhost:3036'; $dbuser = 'root'; $dbpass = 'rootpassword'; $conn = mysql_connect($dbhost, $dbuser, $dbpass); if(! $conn ) { die('Could not connect: ' . mysql_error()); } $sql = 'SELECT tutorial_id, tutorial_title, tutorial_author, submission_date FROM tutorials_tbl'; mysql_select_db('TUTORIALS'); $retval = mysql_query( $sql, $conn ); if(! $retval ) { die('Could not get data: ' . mysql_error()); } while($row = mysql_fetch_array($retval, MYSQL_NUM)) { echo "Tutorial ID :{$row[0]} <br> ". "Title: {$row[1]} <br> ". "Author: {$row[2]} <br> ". "Submission Date : {$row[3]} <br> ". "--------------------------------<br>"; } echo "Fetched data successfully\n"; mysql_close($conn); ?>
All the above three examples will produce same result.
Releasing Memory:
Its a good practice to release cursor memory at the end of each SELECT statement. This can be done by using PHP function mysql_free_result(). Below is the example to show how it has to be used.
Example:
Try out following example
<?php $dbhost = 'localhost:3036'; $dbuser = 'root'; $dbpass = 'rootpassword'; $conn = mysql_connect($dbhost, $dbuser, $dbpass); if(! $conn ) { die('Could not connect: ' . mysql_error()); } $sql = 'SELECT tutorial_id, tutorial_title, tutorial_author, submission_date FROM tutorials_tbl'; mysql_select_db('TUTORIALS'); $retval = mysql_query( $sql, $conn ); if(! $retval ) { die('Could not get data: ' . mysql_error()); } while($row = mysql_fetch_array($retval, MYSQL_NUM)) { echo "Tutorial ID :{$row[0]} <br> ". "Title: {$row[1]} <br> ". "Author: {$row[2]} <br> ". "Submission Date : {$row[3]} <br> ". "--------------------------------<br>"; } mysql_free_result($retval); echo "Fetched data successfully\n"; mysql_close($conn); ?>
While fetching data you can write as complex SQL as you like. Procedure will remain same as mentioned above.
MySQL WHERE Clause
We have seen SQL SELECT command to fetch data from MySQL table. We can use a conditional clause called WHERE clause to filter out results. Using WHERE clause we can specify a selection criteria to select required records from a table.
Syntax:
Here is generic SQL syntax of SELECT command with WHERE clause to fetch data from MySQL table:
SELECT field1, field2,...fieldN table_name1, table_name2... [WHERE condition1 [AND [OR]] condition2.....
- You can use one or more tables separated by comma to include various condition using a WHERE clause. But WHERE clause is an optional part of SELECT command.
- You can specify any condition using WHERE clause.
- You can specify more than one conditions using AND or OR operators.
- A WHERE clause can be used alongwith DELETE or UPDATE SQL command also to specify a condition.
The WHERE clause works like a if condition in any programming language. This clause is used to compare given value with the field value available in MySQl table. If given value from outside is equal to the available field value in MySQL table then it returns that row.
Here is the list of operators which can be used with WHERE clause.
Assume field A holds 10 and field B holds 20 then:
| Operator | Description | Example |
|---|---|---|
| = | Checks if the value of two operands is equal or not, if yes then condition becomes true. | (A = B) is not true. |
| != | Checks if the value of two operands is equal or not, if values are not equal then condition becomes true. | (A != B) is true. |
| > | Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true. | (A > B) is not true. |
| < | Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true. | (A < B) is true. |
| >= | Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true. | (A >= B) is not true. |
| <= | Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true. | (A <= B) is true. |
The WHERE clause is very useful when you want to fetch selected rows from a table, Specially when you use MySQL Join. Joins are discussed in another chapter.
It is a common practice to search records using Primary Key to make search fast.
If given condition does not match any record in the table then query would not return any row.
Fetching Data from Command Prompt:
This will use SQL SELECT command with WHERE clause to fetch selected data from MySQL table tutorials_tbl
Example:
Following example will return all the records from tutorials_tbl table for which author name is Sanjay:
root@host# mysql -u root -p password; Enter password:******* mysql> use TUTORIALS; Database changed mysql> SELECT * from tutorials_tbl WHERE tutorial_author='Sanjay'; +-------------+----------------+-----------------+-----------------+ | tutorial_id | tutorial_title | tutorial_author | submission_date | +-------------+----------------+-----------------+-----------------+ | 3 | JAVA Tutorial | Sanjay | 2007-05-21 | +-------------+----------------+-----------------+-----------------+ 1 rows in set (0.01 sec) mysql>
All the Unless performing a LIKE comparison on a string, the comparison is not case sensitive. You can make your search case sensitive using BINARY keyword as follows.
root@host# mysql -u root -p password; Enter password:******* mysql> use TUTORIALS; Database changed mysql> SELECT * from tutorials_tbl \ WHERE BINARY tutorial_author='sanjay'; Empty set (0.02 sec) mysql>
Fetching Data Using PHP Script:
You can use same SQL SELECT command with WHERE CLAUSE into PHP function mysql_query(). This function is used to execute SQL command and later another PHP function mysql_fetch_array()can be used to fetch all the selected data. This function returns row as an associative array, a numeric array, or both. This function returns FALSE if there are no more rows.
Example:
Following example will return all the records from tutorials_tbl table for which author name is Sanjay:
<?php $dbhost = 'localhost:3036'; $dbuser = 'root'; $dbpass = 'rootpassword'; $conn = mysql_connect($dbhost, $dbuser, $dbpass); if(! $conn ) { die('Could not connect: ' . mysql_error()); } $sql = 'SELECT tutorial_id, tutorial_title, tutorial_author, submission_date FROM tutorials_tbl WHERE tutorial_author="Sanjay"'; mysql_select_db('TUTORIALS'); $retval = mysql_query( $sql, $conn ); if(! $retval ) { die('Could not get data: ' . mysql_error()); } while($row = mysql_fetch_array($retval, MYSQL_ASSOC)) { echo "Tutorial ID :{$row['tutorial_id']} <br> ". "Title: {$row['tutorial_title']} <br> ". "Author: {$row['tutorial_author']} <br> ". "Submission Date : {$row['submission_date']} <br> ". "--------------------------------<br>"; } echo "Fetched data successfully\n"; mysql_close($conn); ?>
MySQL UPDATE Query
There may be a requirement where existing data in a MySQL table need to be modified. You can do so by using SQL UPDATE command. This will modify any field value of any MySQL table.
Syntax:
Here is generic SQL syntax of UPDATE command to modify data into MySQL table:
UPDATE table_name SET field1=new-value1, field2=new-value2 [WHERE Clause]
- You can update one or more field all together.
- You can specify any condition using WHERE clause.
- You can update values in a single table at a time.
The WHERE clause is very useful when you want to update selected rows in a table.
Updating Data from Command Prompt:
This will use SQL UPDATE command with WHERE clause to update selected data into MySQL table tutorials_tbl
Example:
Following example will update tutorial_title field for a record having tutorial_id as 3.
root@host# mysql -u root -p password; Enter password:******* mysql> use TUTORIALS; Database changed mysql> UPDATE tutorials_tbl -> SET tutorial_title='Learning JAVA' -> WHERE tutorial_id=3; Query OK, 1 row affected (0.04 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql>
Updating Data Using PHP Script:
You can use SQL UPDATE command with or without WHERE CLAUSE into PHP functionmysql_query(). This function will execute SQL command in similar way it is executed at mysql> prompt.
Example:
Try out following example to update tutorial_title field for a record having tutorial_id as 3.
<?php $dbhost = 'localhost:3036'; $dbuser = 'root'; $dbpass = 'rootpassword'; $conn = mysql_connect($dbhost, $dbuser, $dbpass); if(! $conn ) { die('Could not connect: ' . mysql_error()); } $sql = 'UPDATE tutorials_tbl SET tutorial_title="Learning JAVA" WHERE tutorial_id=3'; mysql_select_db('TUTORIALS'); $retval = mysql_query( $sql, $conn ); if(! $retval ) { die('Could not update data: ' . mysql_error()); } echo "Updated data successfully\n"; mysql_close($conn); ?>
MySQL DELETE Query
If you want to delete a record from any MySQL table then you can use SQL command DELETE FROM. You can use this command at mysql> prompt as well as in any script like PHP.
Syntax:
Here is generic SQL syntax of DELETE command to delete data from a MySQL table:
DELETE FROM table_name [WHERE Clause]
- If WHERE clause is not specified then all the records will be deleted from the given MySQL table.
- You can specify any condition using WHERE clause.
- You can delete records in a single table at a time.
The WHERE clause is very useful when you want to delete selected rows in a table.
Deleting Data from Command Prompt:
This will use SQL DELETE command with WHERE clause to delete selected data into MySQL table tutorials_tbl
Example:
Following example will delete a record into tutorial_tbl whose tutorial_id is 3.
root@host# mysql -u root -p password; Enter password:******* mysql> use TUTORIALS; Database changed mysql> DELETE FROM tutorials_tbl WHERE tutorial_id=3; Query OK, 1 row affected (0.23 sec) mysql>
Deleting Data Using PHP Script:
You can use SQL DELETE command with or without WHERE CLAUSE into PHP functionmysql_query(). This function will execute SQL command in similar way it is executed at mysql> prompt.
Example:
Try out following example to delete a record into tutorial_tbl whose tutorial_id is 3.
<?php $dbhost = 'localhost:3036'; $dbuser = 'root'; $dbpass = 'rootpassword'; $conn = mysql_connect($dbhost, $dbuser, $dbpass); if(! $conn ) { die('Could not connect: ' . mysql_error()); } $sql = 'DELETE FROM tutorials_tbl WHERE tutorial_id=3'; mysql_select_db('TUTORIALS'); $retval = mysql_query( $sql, $conn ); if(! $retval ) { die('Could not delete data: ' . mysql_error()); } echo "Deleted data successfully\n"; mysql_close($conn); ?>
MySQL LIKE Clause
We have seen SQL SELECT command to fetch data from MySQL table. We can also use a conditional clause called WHERE clause to select required records.
A WHERE clause with equal sign (=) works fine where we want to do an exact match. Like if "tutorial_author = 'Sanjay'". But there may be a requirement where we want to filter out all the results where tutorial_author name should contain "jay". This can be handled using SQL LIKE clause alongwith WHERE clause.
If SQL LIKE clause is used along with % characters then it will work like a meta character (*) in Unix while listing out all the files or directories at command prompt.
Without a % character LIKE clause is very similar to equal sign alongwith WHERE clause.
Syntax:
Here is generic SQL syntax of SELECT command along with LIKE clause to fetch data from MySQL table:
SELECT field1, field2,...fieldN table_name1, table_name2... WHERE field1 LIKE condition1 [AND [OR]] filed2 = 'somevalue'
- You can specify any condition using WHERE clause.
- You can use LIKE clause alongwith WHERE clause.
- You can use LIKE clause in place of equal sign.
- When LIKE is used alongwith % sign then it will work like a meta character search.
- You can specify more than one conditions using AND or OR operators
- A WHERE...LIKE clause can be used alongwith DELETE or UPDATE SQL command also to specify a condition.
Using LIKE clause at Command Prompt:
This will use SQL SELECT command with WHERE...LIKE clause to fetch selected data from MySQL table tutorials_tbl
Example:
Following example will return all the records from tutorials_tbl table for which author name ends withjay:
root@host# mysql -u root -p password; Enter password:******* mysql> use TUTORIALS; Database changed mysql> SELECT * from tutorials_tbl -> WHERE tutorial_author LIKE '%jay'; +-------------+----------------+-----------------+-----------------+ | tutorial_id | tutorial_title | tutorial_author | submission_date | +-------------+----------------+-----------------+-----------------+ | 3 | JAVA Tutorial | Sanjay | 2007-05-21 | +-------------+----------------+-----------------+-----------------+ 1 rows in set (0.01 sec) mysql>
Using LIKE clause inside PHP Script:
You can use similar syntax of WHERE...LIKE clause into PHP function mysql_query(). This function is used to execute SQL command and later another PHP function mysql_fetch_array() can be used to fetch all the selected data if WHERE...LIKE clause is used along with SELECT command.
But if WHERE...LIKE clause is being used with DELETE or UPDATE command then no further PHP function call is required.
Example:
Try out following example to return all the records from tutorials_tbl table for which author name contains jay:
<?php $dbhost = 'localhost:3036'; $dbuser = 'root'; $dbpass = 'rootpassword'; $conn = mysql_connect($dbhost, $dbuser, $dbpass); if(! $conn ) { die('Could not connect: ' . mysql_error()); } $sql = 'SELECT tutorial_id, tutorial_title, tutorial_author, submission_date FROM tutorials_tbl WHERE tutorial_author LIKE "%jay%"'; mysql_select_db('TUTORIALS'); $retval = mysql_query( $sql, $conn ); if(! $retval ) { die('Could not get data: ' . mysql_error()); } while($row = mysql_fetch_array($retval, MYSQL_ASSOC)) { echo "Tutorial ID :{$row['tutorial_id']} <br> ". "Title: {$row['tutorial_title']} <br> ". "Author: {$row['tutorial_author']} <br> ". "Submission Date : {$row['submission_date']} <br> ". "--------------------------------<br>"; } echo "Fetched data successfully\n"; mysql_close($conn); ?>
MySQL Sorting Results
We have seen SQL SELECT command to fetch data from MySQL table. When you select rows, the MySQL server is free to return them in any order, unless you instruct it otherwise by saying how to sort the result. But you sort a result set by adding an ORDER BY clause that names the column or columns you want to sort by.
Syntax:
Here is generic SQL syntax of SELECT command along with ORDER BY clause to sort data from MySQL table:
SELECT field1, field2,...fieldN table_name1, table_name2... ORDER BY field1, [field2...] [ASC [DESC]]
- You can sort returned result on any field provided that filed is being listed out.
- You can sort result on more than one field.
- You can use keyword ASC or DESC to get result in ascending or descending order. By default its ascending order.
- You can use WHERE...LIKE clause in usual way to put condition.
Using ORDER BY clause at Command Prompt:
This will use SQL SELECT command with ORDER BY clause to fetch data from MySQL table tutorials_tbl
Example:
Try out following example which returns result in ascending order.
root@host# mysql -u root -p password; Enter password:******* mysql> use TUTORIALS; Database changed mysql> SELECT * from tutorials_tbl ORDER BY tutorial_author ASC +-------------+----------------+-----------------+-----------------+ | tutorial_id | tutorial_title | tutorial_author | submission_date | +-------------+----------------+-----------------+-----------------+ | 2 | Learn MySQL | Abdul S | 2007-05-24 | | 1 | Learn PHP | John Poul | 2007-05-24 | | 3 | JAVA Tutorial | Sanjay | 2007-05-06 | +-------------+----------------+-----------------+-----------------+ 3 rows in set (0.42 sec) mysql>
Verify all the author names are listed out in ascending order.
Using ORDER BY clause inside PHP Script:
You can use similar syntax of ORDER BY clause into PHP function mysql_query(). This function is used to execute SQL command and later another PHP function mysql_fetch_array() can be used to fetch all the selected data.
Example:
Try out following example which returns result in descending order of tutorial author.
<?php $dbhost = 'localhost:3036'; $dbuser = 'root'; $dbpass = 'rootpassword'; $conn = mysql_connect($dbhost, $dbuser, $dbpass); if(! $conn ) { die('Could not connect: ' . mysql_error()); } $sql = 'SELECT tutorial_id, tutorial_title, tutorial_author, submission_date FROM tutorials_tbl ORDER BY tutorial_author DESC'; mysql_select_db('TUTORIALS'); $retval = mysql_query( $sql, $conn ); if(! $retval ) { die('Could not get data: ' . mysql_error()); } while($row = mysql_fetch_array($retval, MYSQL_ASSOC)) { echo "Tutorial ID :{$row['tutorial_id']} <br> ". "Title: {$row['tutorial_title']} <br> ". "Author: {$row['tutorial_author']} <br> ". "Submission Date : {$row['submission_date']} <br> ". "--------------------------------<br>"; } echo "Fetched data successfully\n"; mysql_close($conn); ?>
Using MySQl Joins
Thus far we have only been getting data from one table at a time. This is fine for simple takes, but in most real world MySQL usage you will often need to get data from multiple tables in a single query.
You can use multiple tables in your single SQL query. The act of joining in MySQL refers to smashing two or more tables into a single table.
You can use JOINS in SELECT, UPDATE and DELETE statements to join MySQL tables. We will see an example of LEFT JOIN also which is different from simple MySQL JOIN.
Using Joins at Command Prompt:
Suppose we have two tables tcount_tbl and tutorials_tbl in TUTORIALS. A complete listing is given below:
Example:
Try out following examples:
root@host# mysql -u root -p password; Enter password:******* mysql> use TUTORIALS; Database changed mysql> SELECT * FROM tcount_tbl; +-----------------+----------------+ | tutorial_author | tutorial_count | +-----------------+----------------+ | mahran | 20 | | mahnaz | NULL | | Jen | NULL | | Gill | 20 | | John Poul | 1 | | Sanjay | 1 | +-----------------+----------------+ 6 rows in set (0.01 sec) mysql> SELECT * from tutorials_tbl; +-------------+----------------+-----------------+-----------------+ | tutorial_id | tutorial_title | tutorial_author | submission_date | +-------------+----------------+-----------------+-----------------+ | 1 | Learn PHP | John Poul | 2007-05-24 | | 2 | Learn MySQL | Abdul S | 2007-05-24 | | 3 | JAVA Tutorial | Sanjay | 2007-05-06 | +-------------+----------------+-----------------+-----------------+ 3 rows in set (0.00 sec) mysql>
Now we can write a SQL query to join these two tables. This query will select all the authors from tabletutorials_tbl and will pickup corresponding number of tutorials fromtcount_tbl.
mysql> SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count -> FROM tutorials_tbl a, tcount_tbl b -> WHERE a.tutorial_author = b.tutorial_author; +-------------+-----------------+----------------+ | tutorial_id | tutorial_author | tutorial_count | +-------------+-----------------+----------------+ | 1 | John Poul | 1 | | 3 | Sanjay | 1 | +-------------+-----------------+----------------+ 2 rows in set (0.01 sec) mysql>
Using Joins in PHP Script:
You can use any of the above mentioned SQL query in PHP script. You only need to pass SQL query into PHP function mysql_query() and then you will fetch results in usual way.
Example:
Try out following example:
<?php $dbhost = 'localhost:3036'; $dbuser = 'root'; $dbpass = 'rootpassword'; $conn = mysql_connect($dbhost, $dbuser, $dbpass); if(! $conn ) { die('Could not connect: ' . mysql_error()); } $sql = 'SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count FROM tutorials_tbl a, tcount_tbl b WHERE a.tutorial_author = b.tutorial_author'; mysql_select_db('TUTORIALS'); $retval = mysql_query( $sql, $conn ); if(! $retval ) { die('Could not get data: ' . mysql_error()); } while($row = mysql_fetch_array($retval, MYSQL_ASSOC)) { echo "Author:{$row['tutorial_author']} <br> ". "Count: {$row['tutorial_count']} <br> ". "Tutorial ID: {$row['tutorial_id']} <br> ". "--------------------------------<br>"; } echo "Fetched data successfully\n"; mysql_close($conn); ?>
MySQL LEFT JOIN:
A MySQL left join is different from a simple join. A MySQL LEFT JOIN gives extra consideration to the table that is on the left.
If I do a LEFT JOIN, I get all records that match in the same way and IN ADDITION I get an extra record for each unmatched record in the left table of the join - thus ensuring (in my example) that every AUTHOR gets a mention:
Example:
Try out following example to understand LEFT JOIN:
root@host# mysql -u root -p password; Enter password:******* mysql> use TUTORIALS; Database changed mysql> SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count -> FROM tutorials_tbl a LEFT JOIN tcount_tbl b -> ON a.tutorial_author = b.tutorial_author; +-------------+-----------------+----------------+ | tutorial_id | tutorial_author | tutorial_count | +-------------+-----------------+----------------+ | 1 | John Poul | 1 | | 2 | Abdul S | NULL | | 3 | Sanjay | 1 | +-------------+-----------------+----------------+ 3 rows in set (0.02 sec)
You would need to do more practice to become familiar with JOINS. This is a but complex concept in MySQL/SQL and will become more clear while doing real examples.
Handling MySQL NULL Values
We have seen SQL SELECT command along with WHERE clause to fetch data from MySQL table. But when we try to give a condition which compare field or column value to NULL it does not work properly.
To handle such situation MySQL provides three operators
- IS NULL: operator returns true of column value is NULL.
- IS NOT NULL: operator returns true of column value is not NULL.
- <=> operator compare values, which (unlike the = operator) is true even for two NULL values
Conditions involving NULL are special. You cannot use = NULL or != NULL to look for NULL values in columns. Such comparisons always fail because it's impossible to tell whether or not they are true. Even NULL = NULL fails.
To look for columns that are or are not NULL, use IS NULL or IS NOT NULL.
Using NULL values at Command Prompt:
Suppose a table tcount_tbl in TUTORIALS database and it contains two columns tutorial_author andtutorial_count, where a NULL tutorial_count indicates that the value is unknown:
Example:
Try out following examples:
root@host# mysql -u root -p password; Enter password:******* mysql> use TUTORIALS; Database changed mysql> create table tcount_tbl -> ( -> tutorial_author varchar(40) NOT NULL, -> tutorial_count INT -> ); Query OK, 0 rows affected (0.05 sec) mysql> INSERT INTO tcount_tbl -> (tutorial_author, tutorial_count) values ('mahran', 20); mysql> INSERT INTO tcount_tbl -> (tutorial_author, tutorial_count) values ('mahnaz', NULL); mysql> INSERT INTO tcount_tbl -> (tutorial_author, tutorial_count) values ('Jen', NULL); mysql> INSERT INTO tcount_tbl -> (tutorial_author, tutorial_count) values ('Gill', 20); mysql> SELECT * from tcount_tbl; +-----------------+----------------+ | tutorial_author | tutorial_count | +-----------------+----------------+ | mahran | 20 | | mahnaz | NULL | | Jen | NULL | | Gill | 20 | +-----------------+----------------+ 4 rows in set (0.00 sec) mysql>
You can see that = and != do not work with NULL values as follows:
mysql> SELECT * FROM tcount_tbl WHERE tutorial_count = NULL; Empty set (0.00 sec) mysql> SELECT * FROM tcount_tbl WHERE tutorial_count != NULL; Empty set (0.01 sec)
To find records where the tutorial_count column is or is not NULL, the queries should be written like this:
mysql> SELECT * FROM tcount_tbl -> WHERE tutorial_count IS NULL; +-----------------+----------------+ | tutorial_author | tutorial_count | +-----------------+----------------+ | mahnaz | NULL | | Jen | NULL | +-----------------+----------------+ 2 rows in set (0.00 sec) mysql> SELECT * from tcount_tbl -> WHERE tutorial_count IS NOT NULL; +-----------------+----------------+ | tutorial_author | tutorial_count | +-----------------+----------------+ | mahran | 20 | | Gill | 20 | +-----------------+----------------+ 2 rows in set (0.00 sec)
Handling NULL Values in PHP Script:
You can use if...else condition to prepare a query based on NULL value.
Example:
Following example take tutorial_count from outside and then compare it with the value available in the table.
<?php $dbhost = 'localhost:3036'; $dbuser = 'root'; $dbpass = 'rootpassword'; $conn = mysql_connect($dbhost, $dbuser, $dbpass); if(! $conn ) { die('Could not connect: ' . mysql_error()); } if( isset($tutorial_count )) { $sql = 'SELECT tutorial_author, tutorial_count FROM tcount_tbl WHERE tutorial_count = $tutorial_count'; } else { $sql = 'SELECT tutorial_author, tutorial_count FROM tcount_tbl WHERE tutorial_count IS $tutorial_count'; } mysql_select_db('TUTORIALS'); $retval = mysql_query( $sql, $conn ); if(! $retval ) { die('Could not get data: ' . mysql_error()); } while($row = mysql_fetch_array($retval, MYSQL_ASSOC)) { echo "Author:{$row['tutorial_author']} <br> ". "Count: {$row['tutorial_count']} <br> ". "--------------------------------<br>"; } echo "Fetched data successfully\n"; mysql_close($conn); ?>
MySQL Regexps
You have seen MySQL pattern matching with LIKE ...%. MySQL supports another type of pattern matching operation based on regular expressions and the REGEXP operator. If you are aware of PHP or PERL then its very simple for you to understand because this matching is very similar to those scripting regular expressions.
Following is the table of pattern which can be used along with REGEXP operator.
| Pattern | What the pattern matches |
|---|---|
| ^ | Beginning of string |
| $ | End of string |
| . | Any single character |
| [...] | Any character listed between the square brackets |
| [^...] | Any character not listed between the square brackets |
| p1|p2|p3 | Alternation; matches any of the patterns p1, p2, or p3 |
| * | Zero or more instances of preceding element |
| + | One or more instances of preceding element |
| {n} | n instances of preceding element |
| {m,n} | m through n instances of preceding element |
Examples:
Now based on above table you can device various type of SQL queries to meet your requirements. Here I'm listing few for your understanding. Consider we have a table called person_tbl and its having a field called name:
Query to find all the names starting with 'st'
mysql> SELECT name FROM person_tbl WHERE name REGEXP '^st';
Query to find all the names ending with 'ok'
mysql> SELECT name FROM person_tbl WHERE name REGEXP 'ok$';
Query to find all the names which contains 'mar'
mysql> SELECT name FROM person_tbl WHERE name REGEXP 'mar';
Query to find all the names starting with a vowel and ending with 'ok'
mysql> SELECT name FROM person_tbl WHERE name REGEXP '^[aeiou]|ok$';
MySQL Transactions
A transaction is a sequential group of database manipulation operations, which is performed as if it were one single work unit. In other words, a transaction will never be complete unless each individual operation within the group is successful. If any operation within the transaction fails, the entire transaction will fail.
Practically you will club many SQL queries into a group and you will execute all of them together as a part of a transaction.
Properties of Transactions:
Transactions have the following four standard properties, usually referred to by the acronym ACID:
- Atomicity: ensures that all operations within the work unit are completed successfully; otherwise, the transaction is aborted at the point of failure, and previous operations are rolled back to their former state.
- Consistency: ensures that the database properly changes states upon a successfully committed transaction.
- Isolation: enables transactions to operate independently of and transparent to each other.
- Durability: ensures that the result or effect of a committed transaction persists in case of a system failure.
In MySQL, transactions begin with the statement BEGIN WORK and end with either a COMMIT or a ROLLBACK statement. The SQL commands between the beginning and ending statements form the bulk of the transaction.
COMMIT and ROLLBACK:
These two keywords Commit and Rollback are mainly used for MySQL Transactions.
- When a successful transaction is completed, the COMMIT command should be issued so that the changes to all involved tables will take effect.
- If a failure occurs, a ROLLBACK command should be issued to return every table referenced in the transaction to its previous state.
You can control the behavior of a transaction by setting session variable called AUTOCOMMIT. If AUTOCOMMIT is set to 1 (the default), then each SQL statement (within a transaction or not) is considered a complete transaction, and committed by default when it finishes. When AUTOCOMMIT is set to 0, by issuing the SET AUTOCOMMIT=0 command, the subsequent series of statements acts like a transaction, and no activities are committed until an explicit COMMIT statement is issued.
You can execute these SQL commands in PHP by using mysql_query() function.
Generic Example on Transaction
This sequence of events is independent of the programming language used; the logical path can be created in whichever language you use to create your application.
You can execute these SQL commands in PHP by using mysql_query() function.
- Begin transaction by issuing SQL command BEGIN WORK
- Issue one or more SQL commands like SELECT, INSERT, UPDATE or DELETE
- Check if there is no error and everything is according to your requirement.
- If there is any error then issue ROLLBACK command otherwise issue a COMMIT command.
Transaction-Safe Table Types in MySQL:
You can not use transactions directly, you can but they would not be save and guaranteed. If you plan to use transactions in your MySQL programming then you need to create your tables in a special way. There are many type of tables which support transactions but most popular one is InnoDB.
Support for InnoDB tables requires a specific compilation parameter when compiling MySQL from source. If your MySQL version does not have InnoDB support, ask your Internet Service Provider to build a version of MySQL with support for InnoDB table types, or download and install the MySQL-Max binary distribution for Windows or Linux/UNIX and work with the table type in a development environment.
If your MySQL installation supports InnoDB tables, simply add a TYPE=InnoDB definition to the table creation statement. For example, the following code creates an InnoDB table called tcount_tbl:
root@host# mysql -u root -p password; Enter password:******* mysql> use TUTORIALS; Database changed mysql> create table tcount_tbl -> ( -> tutorial_author varchar(40) NOT NULL, -> tutorial_count INT -> ) TYPE=InnoDB; Query OK, 0 rows affected (0.05 sec)
Check following link to know more about : InnoDB
You can use other table type like GEMINI or BDB but it depends on your installation if it supports these two types.
MySQL ALTER Command
MySQL ALTER command is very useful when you want to change a name of your table, any table field or if you want to add or delete an existing column in a table.
Lets begin with creation of a table called testalter_tbl
root@host# mysql -u root -p password; Enter password:******* mysql> use TUTORIALS; Database changed mysql> create table testalter_tbl -> ( -> i INT, -> c CHAR(1) -> ); Query OK, 0 rows affected (0.05 sec) mysql> SHOW COLUMNS FROM testalter_tbl; +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | i | int(11) | YES | | NULL | | | c | char(1) | YES | | NULL | | +-------+---------+------+-----+---------+-------+ 2 rows in set (0.00 sec)
Dropping, Adding, or Repositioning a Column:
Suppose you want to drop an existing column i from above MySQL table then you will use DROP clause along with ALTER command as follows
mysql> ALTER TABLE testalter_tbl DROP i;
A DROP will not work if the column is the only one left in the table.
To add a column, use ADD and specify the column definition. The following statement restores the icolumn to testalter_tbl
mysql> ALTER TABLE testalter_tbl ADD i INT;
After issuing this statement, testalter will contain the same two columns that it had when you first created the table, but will not have quite the same structure. That's because new columns are added to the end of the table by default. So even though i originally was the first column in mytbl, now it is the last one:
mysql> SHOW COLUMNS FROM testalter_tbl; +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | c | char(1) | YES | | NULL | | | i | int(11) | YES | | NULL | | +-------+---------+------+-----+---------+-------+ 2 rows in set (0.00 sec)
To indicate that you want a column at a specific position within the table, either use FIRST to make it the first column, or AFTER col_name to indicate that the new column should be placed after col_name. Try the following ALTER TABLE statements, using SHOW COLUMNS after each one to see what effect each one has:
ALTER TABLE testalter_tbl DROP i; ALTER TABLE testalter_tbl ADD i INT FIRST; ALTER TABLE testalter_tbl DROP i; ALTER TABLE testalter_tbl ADD i INT AFTER c;
The FIRST and AFTER specifiers work only with the ADD clause. This means that if you want to reposition an existing column within a table, you first must DROP it and then ADD it at the new position.
Changing a Column Definition or Name:
To change a column's definition, use MODIFY or CHANGE clause along with ALTER command. For example, to change column c from CHAR(1) to CHAR(10), do this:
mysql> ALTER TABLE testalter_tbl MODIFY c CHAR(10);
With CHANGE, the syntax is a bit different. After the CHANGE keyword, you name the column you want to change, then specify the new definition, which includes the new name. Try out following example:
mysql> ALTER TABLE testalter_tbl CHANGE i j BIGINT;
If you now use CHANGE to convert j from BIGINT back to INT without changing the column name, the statement be as expected:
mysql> ALTER TABLE testalter_tbl CHANGE j j INT;
The Effect of ALTER TABLE on Null and Default Value Attributes:
When you MODIFY or CHANGE a column, you can also specify whether or not the column can contain NULL values, and what its default value is. In fact, if you don't do this, MySQL automatically assigns values for these attributes.
Here is the example where NOT NULL column will have value 100 by default.
mysql> ALTER TABLE testalter_tbl -> MODIFY j BIGINT NOT NULL DEFAULT 100;
If you don't use above command then MySQL will fill up NULL values in all the columns.
Changing a Column's Default Value:
You can change a default value for any column using ALTER command. Try out following example.
mysql> ALTER TABLE testalter_tbl ALTER i SET DEFAULT 1000; mysql> SHOW COLUMNS FROM testalter_tbl; +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | c | char(1) | YES | | NULL | | | i | int(11) | YES | | 1000 | | +-------+---------+------+-----+---------+-------+ 2 rows in set (0.00 sec)
You can remove default constraint from any column by using DROP clause along with ALTER command.
mysql> ALTER TABLE testalter_tbl ALTER i DROP DEFAULT; mysql> SHOW COLUMNS FROM testalter_tbl; +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | c | char(1) | YES | | NULL | | | i | int(11) | YES | | NULL | | +-------+---------+------+-----+---------+-------+ 2 rows in set (0.00 sec)
Changing a Table Type:
You can use a table type by using TYPE clause alongwith ALTER command. Try out following example to change testalter_tbl to MYISAM table type.
To find out the current type of a table, use the SHOW TABLE STATUS statement.
mysql> ALTER TABLE testalter_tbl TYPE = MYISAM; mysql> SHOW TABLE STATUS LIKE 'testalter_tbl'\G *************************** 1. row **************** Name: testalter_tbl Type: MyISAM Row_format: Fixed Rows: 0 Avg_row_length: 0 Data_length: 0 Max_data_length: 25769803775 Index_length: 1024 Data_free: 0 Auto_increment: NULL Create_time: 2007-06-03 08:04:36 Update_time: 2007-06-03 08:04:36 Check_time: NULL Create_options: Comment: 1 row in set (0.00 sec)
Renaming a Table:
To rename a table, use the RENAME option of the ALTER TABLE statement. Try out following example to rename testalter_tbl to alter_tbl
mysql> ALTER TABLE testalter_tbl RENAME TO alter_tbl;
You can use ALTER command to create and drop INDEX on a MySQL file. We will see this feature in next chapter.
MySQL INDEXES
A database index is a data structure that improves the speed of operations in a table. Indexes can be created using one or more columns, providing the basis for both rapid random lookups and efficient ordering of access to records.
While creating index it should be considered that what are the columns which will be used to make SQL queries and create one or more indexes on those columns.
Practically, Indexes are also type of tables which keeps primary key or index field and a pointer to each record in to the actual table.
The users cannot see the indexes, they are just used to speed up queries and will be used by Database Search Engine to locate records very fast.
INSERT and UPDATE statements takes more time on tables having indexes where as SELECT statements become fast on those tables. The reason is that while doing insert or update, database need to inert or update index values as well.
Simple and Unique Index:
You can create a unique index on a table. A unique index means that two rows cannot have the same index value. Here is the syntax to create an Index on a table
CREATE UNIQUE INDEX index_name ON table_name ( column1, column2,...);
You can use one or more columns to create an index. For example we can create an index on tutorials_tbl using tutorial_author
CREATE UNIQUE INDEX AUTHOR_INDEX ON tutorials_tbl (tutorial_author)
You can creates a simple index on a table. Just omit UNIQUE keyword from the query to create simple index. Simple index allows duplicate values in a table.
If you want to index the values in a column in descending order, you can add the reserved word DESC after the column name:
mysql> CREATE UNIQUE INDEX AUTHOR_INDEX ON tutorials_tbl (tutorial_author DESC)
ALTER command to add and drop INDEX:
There are four types of statements for adding indexes to a table:
- ALTER TABLE tbl_name ADD PRIMARY KEY (column_list) : This statement adds a PRIMARY KEY, which means that indexed values must be unique and cannot be NULL.
- ALTER TABLE tbl_name ADD UNIQUE index_name (column_list): This statement creates an index for which values must be unique (with the exception of NULL values, which may appear multiple times).
- ALTER TABLE tbl_name ADD INDEX index_name (column_list): This adds an ordinary index in which any value may appear more than once.
- ALTER TABLE tbl_name ADD FULLTEXT index_name (column_list): This creates a special FULLTEXT index that is used for text-searching purposes.
Here is the example to add index in an existing table.
mysql> ALTER TABLE testalter_tbl ADD INDEX (c);
You can drop any INDEX by using DROP clause along with ALTER command. Try out following example to drop above created index.
mysql> ALTER TABLE testalter_tbl DROP INDEX (c);
You can drop any INDEX by using DROP clause along with ALTER command. Try out following example to drop above created inde x.
ALTER Command to add and drop PRIMARY KEY:
You can add primary key as well in the same way. But make sure Primary Key works on columns which are NOT NULL.
Here is the example to add primary key in an existing table. This will make a column NOT NULL first and then add it as a primary key.
mysql> ALTER TABLE testalter_tbl MODIFY i INT NOT NULL; mysql> ALTER TABLE testalter_tbl ADD PRIMARY KEY (i);
You can use ALTER command to drop a primary key as follows:
mysql> ALTER TABLE testalter_tbl DROP PRIMARY KEY;
To drop an index that is not a PRIMARY KEY, you must specify the index name.
Displaying INDEX Information:
You can use SHOW INDEX command to list out all the indexes associated with a table. Vertical-format output (specified by \G) often is useful with this statement, to avoid long line wraparound:
Try out following example:
mysql> SHOW INDEX FROM table_name\G ........
MySQL Temporary Tables
The temporary tables could be very useful in some cases to keep temporary data. The most important thing that should be knows for temporary tables is that they will be deleted when the current client session terminates.
Temporary tables where added in MySQL version 3.23. If you use an older version of MySQL than 3.23 you can't use temporary tables, but you can use heap tables.
As stated earlier temporary tables will only last as long as the session is alive. If you run the code in a PHP script, the temporary table will be destroyed automatically when the script finishes executing. If you are connected to the MySQl database server through the MySQL client program, then the temporary table will exist until you close the client or manually destroy the table.
Example
Here is an example showing you usage of temporary table. Same code can be used in PHP scripts using mysql_query() function.
mysql> CREATE TEMPORARY TABLE SalesSummary ( -> product_name VARCHAR(50) NOT NULL -> , total_sales DECIMAL(12,2) NOT NULL DEFAULT 0.00 -> , avg_unit_price DECIMAL(7,2) NOT NULL DEFAULT 0.00 -> , total_units_sold INT UNSIGNED NOT NULL DEFAULT 0 ); Query OK, 0 rows affected (0.00 sec) mysql> INSERT INTO SalesSummary -> (product_name, total_sales, avg_unit_price, total_units_sold) -> VALUES -> ('cucumber', 100.25, 90, 2); mysql> SELECT * FROM SalesSummary; +--------------+-------------+----------------+------------------+ | product_name | total_sales | avg_unit_price | total_units_sold | +--------------+-------------+----------------+------------------+ | cucumber | 100.25 | 90.00 | 2 | +--------------+-------------+----------------+------------------+ 1 row in set (0.00 sec)
When you issue a SHOW TABLES command then your temporary table would not be listed out in the list. Now if you will log out of the MySQL session and then you will issue a SELECT command then you will find no data available in the database. Even your temporary table would also not exist.
Dropping Temporary Tables:
By default all the temporary tables are deleted by MySQL when your database connection gets terminated. Still you want to delete them in between then you do so by issuing DROP TABLE command.
Following is the example on dropping a temproary table.
mysql> CREATE TEMPORARY TABLE SalesSummary ( -> product_name VARCHAR(50) NOT NULL -> , total_sales DECIMAL(12,2) NOT NULL DEFAULT 0.00 -> , avg_unit_price DECIMAL(7,2) NOT NULL DEFAULT 0.00 -> , total_units_sold INT UNSIGNED NOT NULL DEFAULT 0 ); Query OK, 0 rows affected (0.00 sec) mysql> INSERT INTO SalesSummary -> (product_name, total_sales, avg_unit_price, total_units_sold) -> VALUES -> ('cucumber', 100.25, 90, 2); mysql> SELECT * FROM SalesSummary; +--------------+-------------+----------------+------------------+ | product_name | total_sales | avg_unit_price | total_units_sold | +--------------+-------------+----------------+------------------+ | cucumber | 100.25 | 90.00 | 2 | +--------------+-------------+----------------+------------------+ 1 row in set (0.00 sec) mysql> DROP TABLE SalesSummary; mysql> SELECT * FROM SalesSummary; ERROR 1146: Table 'TUTORIALS.SalesSummary' doesn't exist
MySQL Clone Tables
There may be a situation when you need an exact copy of a table, and CREATE TABLE ... SELECT doesn't suit your purposes because the copy must include the same indexes, default values, and so forth.
You can handle this situation by following steps.
- Use SHOW CREATE TABLE to get a CREATE TABLE statement that specifies the source table's structure, indexes and all.
- Modify the statement to change the table name to that of the clone table and execute the statement. This way you will have exact clone table.
- Optionally, If you need the table contents copied as well, issue an INSERT INTO ... SELECT statement, too.
Example:
Try out following example to create a clone table for tutorials_tbl
Step 1:
Get complete structure about table
mysql> SHOW CREATE TABLE tutorials_tbl \G; *************************** 1. row *************************** Table: tutorials_tbl Create Table: CREATE TABLE `tutorials_tbl` ( `tutorial_id` int(11) NOT NULL auto_increment, `tutorial_title` varchar(100) NOT NULL default '', `tutorial_author` varchar(40) NOT NULL default '', `submission_date` date default NULL, PRIMARY KEY (`tutorial_id`), UNIQUE KEY `AUTHOR_INDEX` (`tutorial_author`) ) TYPE=MyISAM 1 row in set (0.00 sec) ERROR: No query specified
Step 2:
Rename this table and create another table
mysql> CREATE TABLE `clone_tbl` ( -> `tutorial_id` int(11) NOT NULL auto_increment, -> `tutorial_title` varchar(100) NOT NULL default '', -> `tutorial_author` varchar(40) NOT NULL default '', -> `submission_date` date default NULL, -> PRIMARY KEY (`tutorial_id`), -> UNIQUE KEY `AUTHOR_INDEX` (`tutorial_author`) -> ) TYPE=MyISAM; Query OK, 0 rows affected (1.80 sec)
Step 3:
After executing step 2 you will a clone table in your database. If you want to copy data from old table then you can do it by using INSERT INTO... SELECT statement.
mysql> INSERT INTO clone_tbl (tutorial_id, -> tutorial_title, -> tutorial_author, -> submission_date) -> SELECT tutorial_id,tutorial_title, -> tutorial_author,submission_date, -> FROM tutorials_tbl; Query OK, 3 rows affected (0.07 sec) Records: 3 Duplicates: 0 Warnings: 0
Finally you will have exact clone table as you wanted to have
Obtaining and Using MySQL Metadata
There are three information which you would like to have from MySQL.
- Information about the result of queries: This includes number of records effected by any SELECT, UPDATE or DELETE statement.
- Information about tables and databases: This includes information pertaining to the structure of tables and databases.
- Information about the MySQL server: This includes current status of database server, version number etc.
Its very easy to get all these information at mysql prompt. BUt while using PERL or PHP APIs then we need to call various APIs explicitely to obtain all these information. Following section will show you how to obtain these information.
Obtaining the Number of Rows Affected by a Query:
PERL Example:
In DBI scripts, the affected-rows count is returned by do( ) or by execute( ), depending on how you execute the query:
# Method 1 # execute $query using do( ) my $count = $dbh->do ($query); # report 0 rows if an error occurred printf "%d rows were affected\n", (defined ($count) ? $count : 0); # Method 2 # execute query using prepare( ) plus execute( ) my $sth = $dbh->prepare ($query); my $count = $sth->execute ( ); printf "%d rows were affected\n", (defined ($count) ? $count : 0);
PHP Example:
In PHP, invoke the mysql_affected_rows( ) function to find out how many rows a query changed:
$result_id = mysql_query ($query, $conn_id); # report 0 rows if the query failed $count = ($result_id ? mysql_affected_rows ($conn_id) : 0); print ("$count rows were affected\n");
Listing Tables and Databases:
This is very easy to list down all the databases and tables available with database server. Your result may be null if you don't have sufficient privilege.
Apart from the method I have mentioned below you can use SHOW TABLES or SHOW DATABASES queries to get list of tables or databases either in PHP or in PERL.
PERL Example:
# Get all the tables available in current database. my @tables = $dbh->tables ( ); foreach $table (@tables ){ print "Table Name $table\n"; }
PHP Example:
<?php $con = mysql_connect("localhost", "userid", "password"); if (!$con) { die('Could not connect: ' . mysql_error()); } $db_list = mysql_list_dbs($con); while ($db = mysql_fetch_object($db_list)) { echo $db->Database . "<br />"; } mysql_close($con); ?>
Getting Server Metadata:
There are following commands in MySQL which can be executed either are mysql prompt or using any script like PHP to get various important information about database server.
| Command | Description |
|---|---|
| SELECT VERSION( ) | Server version string |
| SELECT DATABASE( ) | Current database name (empty if none) |
| SELECT USER( ) | Current username |
| SHOW STATUS | Server status indicators |
| SHOW VARIABLES | Server configuration variables |
Using MySQL Sequences
A sequence is a set of integers 1, 2, 3, ... that are generated in order on demand. Sequences are frequently used in databases because many applications require each row in a table to contain a unique value, and sequences provide an easy way to generate them. This chapter describes how to use sequences in MySQL.
Using AUTO_INCREMENT column:
The simplest way in MySQL to use Sequences is to define a column as AUTO_INCREMENT and leave rest of the things to MySQL to take care.
Example:
Try out following example. This will create table and after that it will insert few rows in this table where it is not required to give record ID because its auto incremented by MySQL.
mysql> CREATE TABLE insect -> ( -> id INT UNSIGNED NOT NULL AUTO_INCREMENT, -> PRIMARY KEY (id), -> name VARCHAR(30) NOT NULL, # type of insect -> date DATE NOT NULL, # date collected -> origin VARCHAR(30) NOT NULL # where collected ); Query OK, 0 rows affected (0.02 sec) mysql> INSERT INTO insect (id,name,date,origin) VALUES -> (NULL,'housefly','2001-09-10','kitchen'), -> (NULL,'millipede','2001-09-10','driveway'), -> (NULL,'grasshopper','2001-09-10','front yard'); Query OK, 3 rows affected (0.02 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql> SELECT * FROM insect ORDER BY id; +----+-------------+------------+------------+ | id | name | date | origin | +----+-------------+------------+------------+ | 1 | housefly | 2001-09-10 | kitchen | | 2 | millipede | 2001-09-10 | driveway | | 3 | grasshopper | 2001-09-10 | front yard | +----+-------------+------------+------------+ 3 rows in set (0.00 sec)
Obtain AUTO_INCREMENT Values:
LAST_INSERT_ID( ) is a SQL function, so you can use it from within any client that understands how to issue SQL statements. otherwise PERL and PHH scripts provide exclusive functions to retrieve auto incremented value of last record.
PERL Example:
Use the mysql_insertid attribute to obtain the AUTO_INCREMENT value generated by a query. This attribute is accessed through either a database handle or a statement handle, depending on how you issue the query. The following example references it through the database handle:
$dbh->do ("INSERT INTO insect (name,date,origin) VALUES('moth','2001-09-14','windowsill')"); my $seq = $dbh->{mysql_insertid};
PHP Example:
After issuing a query that generates an AUTO_INCREMENT value, retrieve the value by calling mysql_insert_id( ):
mysql_query ("INSERT INTO insect (name,date,origin) VALUES('moth','2001-09-14','windowsill')", $conn_id); $seq = mysql_insert_id ($conn_id);
Renumbering an Existing Sequence:
There may be a case when you have deleted many records from a table and you want to resequence all the records. This can be done by using a simple trick but you should be very careful to do so if your table is having join with other table.
If you determine that resequencing an AUTO_INCREMENT column is unavoidable, the way to do it is to drop the column from the table, then add it again. The following example shows how to renumber the id values in the insect table using this technique:
mysql> ALTER TABLE insect DROP id; mysql> ALTER TABLE insect -> ADD id INT UNSIGNED NOT NULL AUTO_INCREMENT FIRST, -> ADD PRIMARY KEY (id);
Starting a Sequence at a Particular Value:
By default MySQL will start sequence from 1 but you can specify any other number as well at the time of table creation. Following is the example where MySQL will start sequence from 100.
mysql> CREATE TABLE insect -> ( -> id INT UNSIGNED NOT NULL AUTO_INCREMENT = 100, -> PRIMARY KEY (id), -> name VARCHAR(30) NOT NULL, # type of insect -> date DATE NOT NULL, # date collected -> origin VARCHAR(30) NOT NULL # where collected );
Alternatively, you can create the table and then set the initial sequence value with ALTER TABLE.
mysql> ALTER TABLE t AUTO_INCREMENT = 100;
MySQL Handling Duplicates
Tables or result sets sometimes contain duplicate records. Sometime it is allowed but sometime it is required to stop duplicate records. Sometime it is required to identify duplicate records and remove them from the table. This chapter will describe how to prevent duplicate records occurring in a table and how to remove already existing duplicate records.
Preventing Duplicates from Occurring in a Table:
You can use a PRIMARY KEY or UNIQUE Index on a table with appropriate fields to stop duplicate records. Lets take one example, The following table contains no such index or primary key, so it would allow duplicate records for first_name and last_name
CREATE TABLE person_tbl ( first_name CHAR(20), last_name CHAR(20), sex CHAR(10) );
To prevent multiple records with the same first and last name values from being created in this table, add a PRIMARY KEY to its definition. When you do this, it's also necessary to declare the indexed columns to be NOT NULL, because a PRIMARY KEY does not allow NULL values:
CREATE TABLE person_tbl ( first_name CHAR(20) NOT NULL, last_name CHAR(20) NOT NULL, sex CHAR(10) PRIMARY KEY (last_name, first_name) );
The presence of a unique index in a table normally causes an error to occur if you insert a record into the table that duplicates an existing record in the column or columns that define the index.
Use INSERT IGNORE rather than INSERT. If a record doesn't duplicate an existing record, MySQL inserts it as usual. If the record is a duplicate, the IGNORE keyword tells MySQL to discard it silently without generating an error.
Following example does not error out and same time it will not insert duplicate records.
mysql> INSERT IGNORE INTO person_tbl (last_name, first_name) -> VALUES( 'Jay', 'Thomas'); Query OK, 1 row affected (0.00 sec) mysql> INSERT IGNORE INTO person_tbl (last_name, first_name) -> VALUES( 'Jay', 'Thomas'); Query OK, 0 rows affected (0.00 sec)
Use REPLACE rather than INSERT. If the record is new, it's inserted just as with INSERT. If it's a duplicate, the new record replaces the old one:
mysql> REPLACE INTO person_tbl (last_name, first_name) -> VALUES( 'Ajay', 'Kumar'); Query OK, 1 row affected (0.00 sec) mysql> REPLACE INTO person_tbl (last_name, first_name) -> VALUES( 'Ajay', 'Kumar'); Query OK, 2 rows affected (0.00 sec)
INSERT IGNORE and REPLACE should be chosen according to the duplicate-handling behavior you want to effect. INSERT IGNORE keeps the first of a set of duplicated records and discards the rest. REPLACE keeps the last of a set of duplicates and erase out any earlier ones.
Another way to enforce uniqueness is to add a UNIQUE index rather than a PRIMARY KEY to a table.
CREATE TABLE person_tbl ( first_name CHAR(20) NOT NULL, last_name CHAR(20) NOT NULL, sex CHAR(10) UNIQUE (last_name, first_name) );
Counting and Identifying Duplicates:
Following is the query to count duplicate records with first_name and last_name in a table.
mysql> SELECT COUNT(*) as repetitions, last_name, first_name -> FROM person_tbl -> GROUP BY last_name, first_name -> HAVING repetitions > 1;
This query will return a list of all the duplicate records in person_tbl table. In general, to identify sets of values that are duplicated, do the following:
- Determine which columns contain the values that may be duplicated.
- List those columns in the column selection list, along with COUNT(*).
- List the columns in the GROUP BY clause as well.
- Add a HAVING clause that eliminates unique values by requiring group counts to be greater than one.
Eliminating Duplicates from a Query Result:
You can use DISTINCT along with SELECT statement to find out unique records available in a table.
mysql> SELECT DISTINCT last_name, first_name -> FROM person_tbl -> ORDER BY last_name;
An alternative to DISTINCT is to add a GROUP BY clause that names the columns you're selecting. This has the effect of removing duplicates and selecting only the unique combinations of values in the specified columns:
mysql> SELECT last_name, first_name -> FROM person_tbl -> GROUP BY (last_name, first_name);
Removing Duplicates Using Table Replacement:
If you have duplicate records in a table and you want to remove all the duplicate records from that table then here is the procedure.
mysql> CREATE TABLE tmp SELECT last_name, first_name, sex -> FROM person_tbl; -> GROUP BY (last_name, first_name); mysql> DROP TABLE person_tbl; mysql> ALTER TABLE tmp RENAME TO person_tbl;
An easy way of removing duplicate records from a table is that add an INDEX or PRIMAY KEY to that table. Even if this table is already available you can use this technique to remove duplicate records and you will be safe in future as well.
mysql> ALTER IGNORE TABLE person_tbl -> ADD PRIMARY KEY (last_name, first_name);
MySQL and SQL Injection
If you take user input through a webpage and insert it into a MySQL database there's a chance that you have left yourself wide open for a security issue known as SQL Injection. This lesson will teach you how to help prevent this from happening and help you secure your scripts and MySQL statements.
Injection usually occurs when you ask a user for input, like their name, and instead of a name they give you a MySQL statement that you will unknowingly run on your database.
Never trust user provided data, process this data only after validation; as a rule, this is done by pattern matching. In the example below, the username is restricted to alphanumerical chars plus underscore and to a length between 8 and 20 chars - modify these rules as needed.
if (preg_match("/^\w{8,20}$/", $_GET['username'], $matches)) { $result = mysql_query("SELECT * FROM users WHERE username=$matches[0]"); } else { echo "username not accepted"; }
To demonstrate the problem, consider this excerpt:
// supposed input $name = "Qadir'; DELETE FROM users;"; mysql_query("SELECT * FROM users WHERE name='{$name}'");
The function call is supposed to retrieve a record from the users table where the name column matches the name specified by the user. Under normal circumstances, $name would only contain alphanumeric characters and perhaps spaces, such as the string ilia. But here, by appending an entirely new query to $name, the call to the database turns into disaster: the injected DELETE query removes all records from users.
Fortunately, if you use MySQL, the mysql_query() function does not permit query stacking, or executing multiple queries in a single function call. If you try to stack queries, the call fails.
However, other PHP database extensions, such as SQLite and PostgreSQL, happily perform stacked queries, executing all of the queries provided in one string and creating a serious security problem.
Preventing SQL Injection:
You can handle all escape characters smartly in scripting languages like PERL and PHP. The MySQL extension for PHP provides the function mysql_real_escape_string() to escape input characters that are special to MySQL.
if (get_magic_quotes_gpc()) { $name = stripslashes($name); } $name = mysql_real_escape_string($name); mysql_query("SELECT * FROM users WHERE name='{$name}'");
The LIKE Quandary:
To address the LIKE quandary, a custom escaping mechanism must convert user-supplied % and _ characters to literals. Use addcslashes(), a function that let's you specify a character range to escape.
$sub = addcslashes(mysql_real_escape_string("%something_"), "%_"); // $sub == \%something\_ mysql_query("SELECT * FROM messages WHERE subject LIKE '{$sub}%'");
MySQL Database Export - Backup Methods
The simplest way of exporting a table data into a text file is using SELECT...INTO OUTFILE statement that exports a query result directly into a file on the server host.
Exporting Data with the SELECT ... INTO OUTFILE Statement:
The syntax for this statement combines a regular SELECT with INTO OUTFILE filename at the end. The default output format is the same as for LOAD DATA, so the following statement exports the tutorials_tbl table into /tmp/tutorials.txt as a tab-delimited, linefeed-terminated file:
mysql> SELECT * FROM tutorials_tbl -> INTO OUTFILE '/tmp/tutorials.txt';
You can change the output format using options to indicate how to quote and delimit columns and records. To export the tutorial_tbl table in CSV format with CRLF-terminated lines, use this statement:
mysql> SELECT * FROM passwd INTO OUTFILE '/tmp/tutorials.txt' -> FIELDS TERMINATED BY ',' ENCLOSED BY '"' -> LINES TERMINATED BY '\r\n';
The SELECT ... INTO OUTFILE has the following properties:
- The output file is created directly by the MySQL server, so the filename should indicate where you want the file to be written on the server host. There is no LOCAL version of the statement analogous to the LOCAL version of LOAD DATA.
- You must have the MySQL FILE privilege to execute the SELECT ... INTO statement.
- The output file must not already exist. This prevents MySQL from clobbering files that may be important.
- You should have a login account on the server host or some way to retrieve the file from that host. Otherwise, SELECT ... INTO OUTFILE likely will be of no value to you.
- Under Unix, the file is created world readable and is owned by the MySQL server. This means that although you'll be able to read the file, you may not be able to delete it.
Exporting Tables as Raw Data:
The mysqldump program is used to copy or back up tables and databases. It can write table output either as a raw datafile, or as a set of INSERT statements that recreate the records in the table.
To dump a table as a datafile, you must specify a --tab option that indicates the directory where you want the MySQL server to write the file.
For example, to dump the tutorials_tbl table from the TUTORIALS database to a file in the /tmp directory, use a command like this:
$ mysqldump -u root -p --no-create-info \ --tab=/tmp TUTORIALS tutorials_tbl password ******
Exporting Table Contents or Definitions in SQL Format:
To export a table in SQL format to a file, use a command like this:
$ mysqldump -u root -p TUTORIALS tutorials_tbl > dump.txt password ******
This will create file having content as follows:
-- MySQL dump 8.23 -- -- Host: localhost Database: TUTORIALS --------------------------------------------------------- -- Server version 3.23.58 -- -- Table structure for table `tutorials_tbl` -- CREATE TABLE tutorials_tbl ( tutorial_id int(11) NOT NULL auto_increment, tutorial_title varchar(100) NOT NULL default '', tutorial_author varchar(40) NOT NULL default '', submission_date date default NULL, PRIMARY KEY (tutorial_id), UNIQUE KEY AUTHOR_INDEX (tutorial_author) ) TYPE=MyISAM; -- -- Dumping data for table `tutorials_tbl` -- INSERT INTO tutorials_tbl VALUES (1,'Learn PHP','John Poul','2007-05-24'); INSERT INTO tutorials_tbl VALUES (2,'Learn MySQL','Abdul S','2007-05-24'); INSERT INTO tutorials_tbl VALUES (3,'JAVA Tutorial','Sanjay','2007-05-06');
To dump multiple tables, name them all following the database name argument. To dump an entire database, don't name any tables after the database as follows:
$ mysqldump -u root -p TUTORIALS > database_dump.txt password ******
To backup all the databases available on your host use the following:
$ mysqldump -u root -p --all-databases > database_dump.txt password ******
The --all-databases option is available as of MySQL 3.23.12.
These method can be used to implement a database backup stretegy.
Copying Tables or Databases to Another Host:
If you want to copy tables or databases from one MySQL server to another then use mysqldump with database name and table name.
Run the following command at source host. This will dump complete database into dump.txt file:
$ mysqldump -u root -p database_name table_name > dump.txt password *****
You can copy complete database without using a particular table name as explained above.
Now ftp dump.txt file on another host and use the following command. Before running this command, make sure you have created database_name on destination server.
$ mysql -u root -p database_name < dump.txt password *****
Another way to accomplish this without using an intermediary file is to send the output of mysqldump directly over the network to the remote MySQL server. If you can connect to both servers from the host where the cookbook database resides, use this command:
$ mysqldump -u root -p database_name \ states | mysql -h other-host.com database_name
The mysqldump half of the command connects to the local server and writes the dump output to the pipe. The mysql half of the command connects to the remote MySQL server on otherhost.com. It reads the pipe for input and sends each statement to the other-host.com server.
MySQL Database Import - Recovery Methods
There are two simple ways in MySQL to load data into MySQL database from a previously backed up file.
Importing Data with LOAD DATA:
MySQL provides a LOAD DATA statement that acts as a bulk data loader. Here's an example statement that reads a file dump.txt from your current directory and loads it into the table mytbl in the current database:
mysql> LOAD DATA LOCAL INFILE 'dump.txt' INTO TABLE mytbl;
- If the LOCAL keyword is not present, MySQL looks for the datafile on the server host using looking into absolute pathname fully specifies the location of the file, beginning from the root of the filesystem. MySQL reads the file from the given location.
- By default, LOAD DATA assumes that datafiles contain lines that are terminated by linefeeds (newlines) and that data values within a line are separated by tabs.
- To specify a file format explicitly, use a FIELDS clause to describe the characteristics of fields within a line, and a LINES clause to specify the line-ending sequence. The following LOAD DATA statement specifies that the datafile contains values separated by colons and lines terminated by carriage returns and new line character:
mysql> LOAD DATA LOCAL INFILE 'dump.txt' INTO TABLE mytbl -> FIELDS TERMINATED BY ':' -> LINES TERMINATED BY '\r\n';
- LOAD DATA assumes the columns in the datafile have the same order as the columns in the table. If that's not true, you can specify a list to indicate which table columns the datafile columns should be loaded into. Suppose your table has columns a, b, and c, but successive columns in the datafile correspond to columns b, c, and a. You can load the file like this:
mysql> LOAD DATA LOCAL INFILE 'dump.txt' -> INTO TABLE mytbl (b, c, a);
Importing Data with mysqlimport
MySQL also includes a utility program named mysqlimport that acts as a wrapper around LOAD DATA so that you can load input files directly from the command line.
To load a data from dump.txt into mytbl use following command at UNIX prompt.
$ mysqlimport -u root -p --local database_name dump.txt password *****
If you use mysqlimport, command-line options provide the format specifiers. mysqlimport commands that correspond to the preceding two LOAD DATA statements look like this:
$ mysqlimport -u root -p --local --fields-terminated-by=":" \ --lines-terminated-by="\r\n" database_name dump.txt password *****
The order in which you specify the options doesn't matter for mysqlimport, except that they should all precede the database name.
The mysqlimport statement uses the --columns option to specify the column order:
$ mysqlimport -u root -p --local --columns=b,c,a \ database_name dump.txt password *****
Handling Quotes and Special Characters:
The FIELDS clause can specify other format options besides TERMINATED BY. By default, LOAD DATA assumes that values are unquoted, and interprets the backslash (\) as an escape character for special characters. To indicate the value quoting character explicitly, use ENCLOSED BY; MySQL will strip that character from the ends of data values during input processing. To change the default escape character, use ESCAPED BY.
When you specify ENCLOSED BY to indicate that quote characters should be stripped from data values, it's possible to include the quote character literally within data values by doubling it or by preceding it with the escape character. For example, if the quote and escape characters are " and \, the input value "a""b\"c" will be interpreted as a"b"c.
For mysqlimport, the corresponding command-line options for specifying quote and escape values are --fields-enclosed-by and --fields-escaped-by
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