Check Function

Hi guys,
I am quite new to PHP and MySQL. I have created a form for a booking form and i want to check the username is valid against one in the database. If it is not valid i would like an error message to come up. Does anyone know the syntax for this?

 

$username = $_POST['user']; //Gets username from the form
$query = mysql_query("SELECT * FROM `tablename` WHERE `user` = $username"); //Searches table "tablename" for user
$num = mysql_affected_rows($query);//Counts the amount of rows returned/affected
if($num != 0 ){ //if # of rows affected is not equal to 0
 echo "user found!"; //user found
}else{ //otherwise
 echo "user NOT found!"; //user not found
}

PHP:

 

small issue: sql injection

use this code instead

$query = mysql_query("SELECT * FROM `tablename` WHERE `user` = '".mysql_real_escape_string(stripslashes($username))."');

PHP:

Another issue

In your case (SELECT command) instead of mysql_affected_rows, use mysql_num_rows($query);