PHP MySQL script

1. Use empty() insted of isset() ; 
 
Isset() checks if a variable has a value including ( Flase , 0 , or Empty string) , But not NULL. 
In other words, a variable is set if it has been assigned a value other than NULL.

On the other hand the empty() function checks if the variable has an empty value empty string , 0, NULL ,or False. 
Returns FALSE if var has a non-empty and non-zero value. 
 
In other words, a variable is empty if it is an empty string, 0, “0″, false, NULL, array(), and an unset variable are all empty. 

<?php
        $var = NULL;
        
        if(isset($var)){
            echo " I am set". PHP_EOL;            
        }
        
        if(empty($var)){
            echo " I am empty". PHP_EOL;
        }
 ?>
 
 Output : 
        
        I am empty

 <?php
 
        $var = '';
         
        if(isset($var)){
            echo " I am set". PHP_EOL;
        }
         
        if(empty($var)){
            echo " I am empty". PHP_EOL;
        } 
        
?>

 Output : 
    I am set
    I am empty

Note: Now when you are validating forms to make sure a user did not leave a form field blank, it is probably best to use neither empty() or isset(). Since it is possible your form might accept 0 as a valid answer. Therefore you should just check to make sure it is not an empty string.

 
<?php

if($_GET['var'] == "") {
    echo "You must enter a value for var!". PHP_EOL;
}
?>