How to run a sql query inside a while of another sql query?

Question

Hi my code as follow:-

$sql="SELECT student_id,DA1,DA2,DA3,DA4,DA5,DA6,HA1,HA2,HA3,HA4,HA5,HA6 from table";
$results = $result->query($sql);
while($row = $results->fetch_assoc())
{
   $id = $row['student_id'];
   $marks1 = $row['DA1'] + $row['HA1']/2 ;
   $marks2 = $row['DA2'] + $row['HA2']/2 ;
   $marks3 = $row['DA3'] + $row['HA3']/2 ;
   $marks4 = $row['DA4'] + $row['HA4']/2 ;
   $marks5 = $row['DA5'] + $row['HA5']/2 ;
   $marks6 = $row['DA6'] + $row['HA6']/2 ;

   $i = 1;
   while($i <= 6)
   {
      $sql = "SELECT `grade`,`point` FROM `grades` where  ${'marks' . $i} BETWEEN min and max";
      $results = $result->query($sql);
      $row = $results->fetch_assoc();
      ${'grade' . $i} = $row['grade'];
      ${'point' . $i} = $row['point'];
      $i++;
    }  

    $totalcredit = 20;
    $sgpa= ($point1*$c1 + $point2*$c2 + $point3*$c3 + $point4*$c4 + $point5*$c5 + $point6*$c6) / $totalcredit ;

    $sql = "UPDATE table SET `G1` = '$grade1', `G2` = '$grade2' ,`G3` ='$grade3',`G4` = '$grade4',`G5` = '$grade5',`G6` = '$grade6', `SGPA` = '$sgpa' WHERE student_id = '$id'";
    $result->query($sql);
 }

In this code i am trying to calculate grade and sgpa of a class. In the first query selecting all the details and calulating total marks in six subjects. In the second query i am storing the grade and point in variables with respect to the marks and then calculating the sgpa. Then the update query is performed to store the details in database.

The table consist of 100 rows. The code is working for the first row but does not work for another rows and returns empty values. I am recursively trying to calculate and update the table with data of all students. I would be highly grateful if anybody can help in running the code for all the rows.

Answer 1

Change the inner while loop like this:-

$i = 1;
while($i <= 6)
{
  $sql = "SELECT `grade`,`point` FROM `grades` where  ${'marks' . $i} BETWEEN min and max";
  $results2 = $result->query($sql);
  $row = $results2->fetch_assoc();
  ${'grade' . $i} = $row['grade'];
  ${'point' . $i} = $row['point'];
  $i++;
}

In your code $results is getting overrided so changing it to $results2 in inner loop will solve your problem.