MySQL
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. This tutorial gives an initial push to start
you with MySQL.
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.
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.
4. 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
|
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.
[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 moment 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 |
+----------+ 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";
[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.
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@hoat#
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@hoat#
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.
This tutorial focuses heavily on
using MySQL in a PHP environment. If you are interested in MySQL with PERL then
you can look into PERL and MySQL
Tutorial.
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>
|
Starting from next chapter we
will see all the important MySQL functionality along with PHP.
MySQL Database Connection
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
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 TUTORIALSEnter 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 );
|
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
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 command use
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 TABLE to 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.
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>
|
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>
|
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>
|
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>
|
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