How can I save time to run sql query? - php

Question

I am a newbie and have very minimum experience to work with php and sql. I have tried the below code but it takes very large amount of time to run.
For each member of the students6 table, his/her Name and Registration number is collected from another table collegestudents and this process takes so much time that server gives
503 error
when students6 table contains huge amount of data. How can the code be changed
to accelerate the process?
$no1=0;
$zq1=mysqli_query($con, "select *
from students6
where CollegeCode='$college'
order by UniversityRollNo");
while($zq2=mysqli_fetch_array($zq1)) {
$xpa=mysqli_query($con, "select *
from collegestudents
where UniversityRollNo='$zq2[UniversityRollNo]'
and CollegeCode='$college'");//
$xp1a=mysqli_fetch_array($xpa);
$name=$xp1a['Name'];
$rgn=$xp1a['RegistrationNo'];
++$no1;
echo "<tr>
<td align='center' >$no1</td><td>$zq2[UniversityRollNo]</td>
<td>$name</td>
<td>$rgn</td>
<td>$zq2[SubjectPaper]</td>
<td align='center'>$zq2[Course]</td>
</tr>";
}

Answer 1

Do both queries in one JOINED query
$no1=0;
$stmt = $con->prepare("select *
from students6 s
JOIN collegestudents c ON c.UniversityRollNo = s.UniversityRollNo
where s.CollegeCode = ?
order by s.UniversityRollNo");
$stmt->bind_param('i',$CollegeCode); //<-- assumed that was holding the code????
$stmt->execute();
$results = $stmt->get_result();
while($zq2 = $results->fetch_assoc){
$name = $xp1a['Name'];
$rgn = $xp1a['RegistrationNo'];
++$no1;
echo "<tr>
<td align='center' >$no1</td><td>$zq2[UniversityRollNo]</td>
<td>$name</td>
<td>$rgn</td>
<td>$zq2[SubjectPaper]</td>
<td align='center'>$zq2[Course]</td>
</tr>";
}