Sql rating issue - php

Question

Here's my code. My problem is that I want the insertion to happen just when the rating_airlines value is between 1 and 5 but it keeps adding all the values.
rating_airlines is varchar on my database.
<?php
require_once('connect.php');
mysql_select_db($database_localhost,$con);
$nom_airlines=$_GET['nom_airlines'];
$rating_airlines=$_GET['rating_airlines'];
$a=intval($rating_airlines);
if($a=1 || $a=2 || $a=3 || $a=4 || $a=5 ) {
mysql_query("INSERT INTO Airlines(nom_airlines,rating_airlines)
VALUES ('$nom_airlines','$a') ");
echo "OK";}
else {
die('Requête invalide : ' . mysql_error());
}
?>

Answer 1

You're not comparing the values you are setting. Single equals sets double compares.
if($a=1 || $a=2 || $a=3 || $a=4 || $a=5 )
Should be
if($a==1 || $a==2 || $a==3 || $a==4 || $a==5 )
But could even be
if($a>=1 && $a <=5 )
You also should switch from the mysql to mysqli or PDO. mysqli or PDO - what are the pros and cons?
Also note that by passing $nom_airlines directly to your query you are open to injections at a minimum use the mysql_real_escape_string.
$nom_airlines=mysql_real_escape_string($_GET['nom_airlines']);

Answer 2

You are using assigning operator . You need to use equality here.
if($a==1 || $a==2 || $a==3 || $a==4 || $a==5 ) {
Take a look into these 2:
Assignment Operators in PHP
Equality Operators in PHP
Moreover,
$a = $b Assign Sets $a to be equal to $b.
$a == $b Equal TRUE if $a is equal to $b.
$a === $b Identical TRUE if $a is equal to $b, and they are of the same type. (introduced in PHP 4)