Php Mysql Introduction

PHP MySQL :

MySQL is the most popular open source database server.

What is MySQL :

MySQL is a database. A database defines a structure for storing information. In a database, there are tables. Just like HTML tables, database tables contain rows, columns, and cells.

Databases are useful when storing information categorically. A company may have a database with the following tables: "Employees", "Products", "Customers" and "Orders".

Database Tables :

A database most often contains one or more tables. Each table has a name (e.g. "Customers" or "Orders"). Each table contains records (rows) with data.

Below is an example of a table called "Persons":

The table above contains three records (one for each person) and four columns (LastName, FirstName, Address, and City).

Queries :

A query is a question or a request.

With MySQL, we can query a database for specific information and have a recordset returned.

Look at the following query:

SELECT LastName FROM Persons

The query above selects all the data in the LastName column in the Persons table, and will return a recordset like this:

LastName
Hansen
Svendson
Pettersen

Download MySQL Database :

If you don't have a PHP server with a MySQL Database, you can download MySQL for free here:

http://www.mysql.com/downloads/index.html

Facts About MySQL Database :

One great thing about MySQL is that it can be scaled down to support embedded database applications. Perhaps it is because of this reputation that many people believe that MySQL can only handle small to medium-sized systems.

The truth is that MySQL is the de-facto standard database for web sites that support huge volumes of both data and end users (like Friendster, Yahoo, Google). Look at http://www.mysql.com/customers/ for an overview of companies that use MySQL.

PHP MySQL Connect to a Database :

The free MySQL Database is very often used with PHP.

Before you can access and work with data in a database, you must create a connection to the database.

In PHP, this is done with the mysql_connect() function.

//Syntax
 mysql_connect(servername,username,password);

Example :

In the following example we store the connection in a variable ($con) for later use in the script.

The "die" part will be executed if the connection fails:

<?php
$con = mysql_connect("localhost","peter","abc123");
if (!$con)
{
die("Could not connect: " . mysql_error());
}
// some code
?>

Closing a Connection :

The connection will be closed as soon as the script ends. To close the connection before, use the mysql_close() function.

<?php
$con = mysql_connect("localhost","peter","abc123");
if (!$con)
{
die("Could not connect: " . mysql_error());
}
// some code
mysql_close($con);
?>

PHP MySQL Create Database and Tables :

A database holds one or multiple tables.

The CREATE DATABASE statement is used to create a database in MySQL.

//Syntax
 CREATE DATABASE database_name

To get PHP to execute the statement above we must use the mysql_query() function. This function is used to send a query or command to a MySQL connection.

Example

In the following example we create a database called "my_db":

<?php
$con = mysql_connect("localhost","peter","abc123");
if (!$con)
{
die("Could not connect: " . mysql_error());
}
if (mysql_query("CREATE DATABASE my_db",$con))
{
echo "Database created";
}
else
{
echo "Error creating database: " . mysql_error();
}
mysql_close($con);
?>

The CREATE TABLE statement is used to create a database table in MySQL.

//Syntax
CREATE TABLE table_name
(
column_name1 data_type,
column_name2 data_type,
column_name3 data_type,
.......
)

We must add the CREATE TABLE statement to the mysql_query() function to execute the command.

Example The following example shows how you can create a table named "person", with three columns. The column names will be "FirstName", "LastName" and "Age":

<?php
$con = mysql_connect("localhost","peter","abc123");
if (!$con)
{
die("Could not connect: " . mysql_error());
}
// Create database
if (mysql_query("CREATE DATABASE my_db",$con))
{
echo "Database created";
}
else
{
echo "Error creating database: " . mysql_error();
}
// Create table in my_db database
mysql_select_db("my_db", $con);
$sql = "CREATE TABLE person
(
FirstName varchar(15),
LastName varchar(15),
Age int
)";
mysql_query($sql,$con);
mysql_close($con);
?>

Important: A database must be selected before a table can be created. The database is selected with the mysql_select_db() function.

Note: When you create a database field of type varchar, you must specify the maximum length of the field, e.g. varchar(15).

Below is the different MySQL data types that can be used:

Primary Keys and Auto Increment Fields :

Each table should have a primary key field.

A primary key is used to uniquely identify the rows in a table. Each primary key value must be unique within the table. Furthermore, the primary key field cannot be null because the database engine requires a value to locate the record.

The primary key field is always indexed. There is no exception to this rule! You must index the primary key field so the database engine can quickly locate rows based on the key's value.

The following example sets the personID field as the primary key field. The primary key field is often an ID number, and is often used with the AUTO_INCREMENT setting.

AUTO_INCREMENT automatically increases the value of the field by 1 each time a new record is added. To ensure that the primary key field cannot be null, we must add the NOT NULL setting to the field.

Example :

$sql = "CREATE TABLE person
(
personID int NOT NULL AUTO_INCREMENT,
PRIMARY KEY(personID),
FirstName varchar(15),
LastName varchar(15),
Age int
)";
mysql_query($sql,$con);