How to remove duplication in the retrieval results? - php

Question

Please i need a help am beginner in php and my sql, i want to retrieve all students names who registered in each level(1 OR 2 OR 3 OR 4) this is my code.
<form id="form1" name="form1" method="post" action="">
<table border="1" align="center" class="tftable">
<?php
$lvlid = $_GET['id'];
$sql2 = "select * from `course` where acadlevel='$lvlid' ";
$res2= mysql_query($sql2,$con_mark_entry);
while($row2 = mysql_fetch_row($res2))
{?>
<?php } ?>
<tr>
<th id="h7">Serial NO.</th>
<th id="h7">Student NO.</th>
<th id="h7">Student Name</th>
</tr>
<?php
$s=1;
$sql ="SELECT student.stud_id,student.stud_name, course.title, enrollment.grade FROM student, course, enrollment WHERE course.acadlevel ='".$_GET['id'] ."' AND course.code = enrollment.code AND student.stud_id = enrollment.stud_id";
$res= mysql_query($sql,$con_mark_entry);
while($row1 = mysql_fetch_row($res)){
?>
<tr>
<td><?php echo $s?> </td>
<td><?php echo $row1[0]?></td>
<td id="name"><a href="report6.php?id=<?php echo $row1[1]?>"> <?php echo $row1[1]?> </td>
</tr>
<?php
$s++;
}
?>
</table>
My Problem is for example if the student registered in three course at level 1 ,he would appear three times, i want to remove this duplication. HOW?
The result as follow:
serial no student no student name
1 101 adam nagdy
2 101 adam nagdy
3 101 adam nagdy
4 102 shima najm
Thanks in advance

Answer 1

Use DISTINCT keyword. It removes duplicate result rows.
Search for "distinct" in this page.
SELECT DISTINCT std.stud_id,std.stud_name, enr.grade -- , crs.title
FROM student std
LEFT OUTER JOIN enrollment enr ON std.stud_id = enr.stud_id
LEFT OUTER JOIN course crs ON crs.code = enr.code
WHERE course.acadlevel ='YOUR_ID'
And use JOIN to join. ;) It is better than joining with WHERE (even if it works).

Answer 2

Try using GROUP BY course.acadlevel at the end of your query.
That should reduce the results to one row per academic level, instead of 3, if the student registered for 3 classes.
Also, as John Conde has commented, mysql_ prefixed functions are deprecated and will be removed from future versions of PHP. You should instead use Mysqli or PDO_MySQL. And you should never use $_GET[]/$_POST or any other variables with user input in your MySQL queries without sanitizing them.