The first parameter $server which we have passed, is the address of MySQL server to connect using the username and password provided by the $username and $password parameters.

How to close a Database Connection

Though not strictly necessary, sometimes it is advantageous to close an open connection to the database when it is no longer needed, Instead of waiting for an end of the request, while PHP will do so automatically. The syntax of mysql_close() function is as follows.

mysql_close($link)

where the parameter $link is the database connection resource returned from the mysql_connect() function.

How to select the Database to Use?

Once you have set up a database connection, the next step is to select the database on which you willbe performing queries(This is similar to SQL USE). To do so, you need the mysql_select_db() function which has the following syntax:

mysql_select_db($database , $link);

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

mysql_select_db("my_db", $con);

mysql_close($con);
?>

Here $my_db is the name of database, and the other parameter $con which is optional is the database connection resource returned by the mysql_connect() function. This function attempts to select the specified database and return a Boolean value indicating the success or failure.

How to perform Query against a Database

To perform a query against the database within PHP, we make use of mysql_query() function, whose syntax is as follows:

mysql_query($query , $link);

where $result holds the result of the query executed. Query is written inside the mysql_query function(without the terminating semi-colon or \g), the optional parameter $con is the value returned by the function mysql_connect(). And if the database is not closed, then PHP will use the last opened connection.

How to retrieving a Result Set?

PHP has many different methods to access the data from a result set, but they all have the same general form. Here we are showing the examle with the context of mysql_fetch_row() function. Its syntax is as follows:

mysql_query($query , $link);

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

mysql_select_db("my_db", $con);
$result = mysql_query("SELECT * FROM person");
while($row = mysql_fetch_array($result))
{
echo $row['FirstName'] . " " . $row['LastName'];
echo "<br />";
}
mysql_close($con);
?>

where $result holds the result returned from a successful query executed using the function mysql_query(). This function returns a single row from the result set when called , in the form of enumerated array, where element "0" represents the first column, element "1" represents the second, and so on. Each subsequent call to the funtion will return the subsequent row in the result set until no row remains. Then the function mysql_fetch_row() returns a boolean false. Generally mysql_fetch_row() function is used in conjunction with the while loop to retrieve the entire array as shown in the above example.