Multiple update queries using loop in PHP & MySQL

Question

I have a table wherein I store the list of students enrolled in a class, and also their respective grades. It has STUD_ID and STUD_GRADE as columns, and the default value of the STUD_GRADE is NA.

What I want to do is to display all the students in the table, and a textbox for their grades beside them, and when the submit button is pressed, then all of the rows would be updated.

I display them all by using this code:

    $query = "SELECT stud_id FROM tblgrade";
    $result = mysql_query($query,$db) or die (mysql_error($db));
    while($row = mysql_fetch_array($result))
    {
        extract($row);

        echo "<tr><td><input type='hidden' value='$stud_id' name='id'/> stud_id </td>
        <td><input type='text' size='10' name='grade'></td>
        <tr>";
    }

    ?>

What I am trying to do is to update the NA grades by using a loop in either the query itself or PHP functions. I tried so many things already but I'm really having difficulties in making the proper loop. It always give out a result wherein only the last row would be updated.

Here is the first and last thing I tried to work on:

    $query = "SELECT stud_id FROM tblgrade";
    $result = mysql_query($query,$db) or die (mysql_error($db));
    while($row = mysql_fetch_array($result))
    {
    $query1 = "UPDATE tblgrade SET stud_grade = '$_POST[grade]' WHERE stud_id = '$_POST[id]'";
    mysql_query($query1,$db) or die (mysql_error($db));
    }
    echo "Grades have been updated!";

I choose not to post the loops I tried, because they are all really messed up, and I am hoping something like the one I posted above can be done.

Suggestions, anyone? Thanks in advance. :D

PS: Really not good at looping.. :(

Answer 1

i would do it like this:

UPDATE tblgrade
    SET stud_grade = CASE 
        WHEN stud_id_1_value THEN 'stud_grade_1_value'
        WHEN stud_id_2_value THEN 'stud_grade_2_value'
        WHEN stud_id_3_value THEN 'stud_grade_3_value'
        ...
    END
WHERE stud_id IN (stud_id_1_value,stud_id_2_value,stud_id_3_value,...);