Variable trouble with mysql and php

I am using hidden fields to transfer variables from several pages to this one "email.php" page.
The variable is called $class.
And the page holds the following query :

 $sql = " select student_email.student_id, student_email.info_2, student_email.info_3, student_email.info_3, '$class'
	from student_email, AllClasses 
	where student_email.student_id = AllClasses.student_id
	and $class = 1";

Code (markup):

This query doesnt work, but it works if I leave the first '$class' (after student_email.info_3) and replace the second (at the very end of the query) with the actual column name.
I don't understand why it would work in the first part but not the second (and I have tried putting it as '$class' = 1 with no such luck either).

 

You have wrong query

 $sql = "select student_email.student_id, student_email.info_2, student_email.info_3, student_email.info_3, `$class`
	from student_email, AllClasses 
	where student_email.student_id = AllClasses.student_id
	and $class = 1";

PHP:

Better

sprintf("select student_email.student_id, student_email.info_2, student_email.info_3, student_email.info_3, %s
	from student_email, AllClasses 
	where student_email.student_id = AllClasses.student_id
	and %s = 1",mysql_real_escape_string($class),mysql_real_escape_string($class));

PHP:

 

what's the variable type of $class? if its not integer use single quotes e.g. '$class' = '1'

 

You can't use single quotes with the field. but this `$class`='1'

 

$class is a variable so we can do single quote.

 

Thanks guys, I've tried all of your suggestions, unfortunately none of them are working :/

I changed the "error query database" to mysql error and it came back with this as the problem

"You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'from student_email, AllClasses where student_email.student_id = AllClasses.stu' at line 1"

so PF is getting changed to stu?

 

Okay, fixed.

The problem was that because the form and the php were all in the one document, and because I was using hidden fields for variables (coming from the previous page) I had to declare the variable again in the second form.