List Down All Non-Paid Students But Having Some Issue - php

Question

I am trying to list down all the students who dont pay their dues between two date ranges. I first select all the student ids from fee table and then store it in a variable and then compare these ids with student table to list down all non paid students. But my problem is it works only on last id. Let say if i get student id, 1 and 2 then query works only on student id 2. Here is the code.
$query = mysql_query("SELECT student_id,created FROM fee WHERE DATE(created) between '$sqldate1' AND '$sqldate2'");
while($rows = mysql_fetch_array($query)) {
$students = $rows['student_id'];
//echo $students;
$link = mysql_query("SELECT fee.class_id,fee.section_id,fee.student_id,fee.section_group,
fee.student_fee,fee.test_fee,fee.other_charges,fee.created,fee.fee_month,
class.class_id,class.class_name,section.section_id,section.section_name,student.id,
student.student_name FROM fee LEFT JOIN class ON(fee.class_id=class.class_id)
LEFT JOIN section ON(fee.section_id=section.section_id)
LEFT JOIN student ON(fee.student_id=student.id) WHERE student.id !='$students'")
or die(mysql_error());
$num = mysql_num_rows($link);
}

Answer 1

You must specify the table name on the join condition as mentioned below
$link = mysql_query("SELECT fee.class_id,fee.section_id,fee.student_id,fee.section_group,
fee.student_fee,fee.test_fee,fee.other_charges,fee.created,fee.fee_month,
class.class_id,class.class_name,section.section_id,section.section_name,student.id,
student.student_name FROM fee LEFT JOIN class ON(fee.class_id=class.class_id)
LEFT JOIN section ON(fee.section_id=section.section_id)
LEFT JOIN student ON(fee.student_id=student.id) WHERE DATE(fee.created) between '$sqldate1' AND '$sqldate2'")

Answer 2

You are iterating over every student_id from your initial query, and running your second query using a different, single student each time. Since you are overwriting $students, $link, and $num each iteration without storing them somewhere, that data is lost and you will be left with whatever the last iteration of your loop happened to be.
You need to first construct a list of all student_ids which you wish to check against, then use that in a comparison in your second query (which needs to be outside of the while loop).

Answer 3

$students is being overwritten in your while loop with each new student id, leaving it with only the last one. Make $students an array:
$students[] = $row['student_id'];
And changr the second query:
WHERE student.id NOT IN (".implode(",", $students).")

Answer 4

You can just have one query:
SELECT fee.class_id,fee.section_id,fee.student_id,fee.section_group,
fee.student_fee,fee.test_fee,fee.other_charges,fee.created,fee.fee_month,
class.class_id,class.class_name,section.section_id,section.section_name,student.id,
student.student_name FROM fee LEFT JOIN class ON(fee.class_id=class.class_id)
LEFT JOIN section ON(fee.section_id=section.section_id)
LEFT JOIN student ON(fee.student_id=student.id) WHERE student.id NOT EXISTS (SELECT student_id,created FROM fee WHERE DATE(created) between '$sqldate1' AND '$sqldate2');