PHP Tutorial–Lesson 5: Introduction to PHP- Part I

PHP and MySQL

•Our previous examples focused on how to write correct MySQL syntax.

•Now, we are going to learn how to take advantages of MySQL queries in our PHP applications.

•PHP, offers number of built-in functions that deal with MySQL db.

•These functions communicate with MySQL db. and allow us to run MySQL queries through PHP Script.

Connectivity to MySQL

•Before getting access to database, we had to start a connection with the server where it lies on.

•To start a connection between your script and db. PHP offers function mysql_connect().

•This function takes three parameters, first one is MySQL server address. Second one is username for the user of the db. And last one is password for that user.

Example

mysql_connect(“localhost”,”anas”,”1234”);

•A call to mysql_connect() will start a connection with the specified MySQL server and username and password.

•This function returns a value of true or false.

•If the connection succeeded, then it returns true, so you can complete.

•If the connection failed, then it returns false, which means your script will not work well as expected.

•It is important to know whether the connection succeeded or not. And if not, determine where is the error.

•PHP offers a function that tells you what is the MySQL error message for your query.

•It is important to make your script stop working if the connection failed with your db server, this will increase security of your application.

Example:

<?php

$host = “localhost”;

$username = “anas”;

$password = “123”;

$connected = mysql_connect($host,$username,$password);

if(!$connected)

{

die(“Unable to connect to db<br />”.mysql_error() );

}

mysql_close($connected);

?>

Notes:

•$host: is the MySQL server address you want to make connection on.

•$username: is the username of the user who uses the MySQL server.

•$password: is the password of the user who uses the MySQL server.

•$connected: stores the returned value of function mysql_connect. Which is true or false.

•We checked for value of $connected. If it is true, then we can complete our application. Else then we had to stop executing the script, in order to avoid unexpected errors.

•Function die like function exit in C/C++. Its job is stopping the script execution.

•It is important to know what the error that prevented your query succession is. To get this, PHP offers mysql_error() function that returns a string contains the error message that MySQL server responded to you about your query.

•At end of each php script that communicates with MySQL server, it is preferred to close the connection, although this connection will be closed automatically at end of script. It is important to close it manually by calling function mysql_close() with parameter of the connection to be closed.

•Once we had connected to the MySQL server, we have to select which db we want to deal with.

•PHP offers function mysql_select_db() that takes two parameters, first one is database_name, second parameter is the connection.

•This function call comes after starting succeeded connection with db.

<?php

// config.php

$host = “localhost”;

$username=“anas”;

$password=“1234”;

$connected = mysql_connect($host,$username,$password);

if(!$connected) die(“unable to connect to db<br />”.mysql_error());

mysql_select_db(“company”,$connected);

mysql_close($connected);

?>

•To organize your project, and make development acceleration improve smoothly, it is preferred to save previous code in a file called for example: config.php and put this file in a directory named for example include.

•These steps, will save your time, and avoid you write these lines each time you want to connect to your MySQL server. Then include this file in each script you need to communicate with db.

To download this lesson as PDF click here: PHP Tutorial–Lesson 5: Introduction to PHP- Part I

Best Wishes,

Anas Jaghoub

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