dynamic columns using pivot table query

Question

I have this attendance table

---------------------------------------------------------------------------
attendance_id | stud_id      | week       | sy        |sem         |present
---------------------------------------------------------------------------
1             | 1            | 02/18/2012 | 2010-2011 |1st semester|1
2             | 2            | 02/18/2012 | 2010-2011 |1st semester|1
3             | 3            | 02/18/2012 | 2010-2011 |1st semester|1
4             | 1            | 02/25/2012 | 2010-2011 |1st semester|1
5             | 2            | 02/25/2012 | 2010-2011 |1st semester|1
6             | 1            | 03/03/2012 | 2010-2011 |1st semester|1
7             | 2            | 03/03/2012 | 2010-2011 |1st semester|1
8             | 3            | 03/03/2012 | 2010-2011 |1st semester|1

my query is this

Select cadet_record.fname,cadet_record.lname,cadet_record.mname, student_id,

MAX(case WHEN week = '02/18/2012' then present end) as 'week1',
MAX(case WHEN week = '02/25/2012' then present end) as 'week2'
From attendance
LEFT JOIN cadet_record ON cadet_record.stud_no = attendance.student_id WHERE section = '$section' AND schoolyear = '$year' AND component = '$component' AND semester = '$semester'
GROUP BY student_id

how can I dynamically call all the week without inserting the dates for eg 02/28/2012, 02/29/2012 so on and so forth. any ideas? =(

Answer 1

As far as I know, you can't dynamically add columns to a SELECT statement. What you're asking for is a way of presenting data and that is not something MySQL cares about. You should handle that in the front end.

However, you can cheat by creating your queries in your model and dynamically adding those new columns, by dynamically inserting more MAX(case... to the query string. That's not a nice solution, though.

Edit:

Im using php, how can I accomplish that?

So, I guess you're talking about the ugly solution. Well, basically you should dynamically create your query string (pseudocode):

$initialDay = 02/28/2012;
$lastDay = 03/28/2012;
$dayNumber = 1;
$sql = 'Select cadet_record.fname,cadet_record.lname,cadet_record.mname, student_id';
while ($initialDay <= $lastDay) {
    $sql .= ', MAX(case WHEN week = $initialDay then present end) as day' . $dayNumber;
    $initialDay = $initialDay + 1 day;
    $dayNumber++;
}
$sql .= ' From attendance blah blah...';

Then your query should look like this for dates from 02/18/2012 to 03/18/2012:

Select cadet_record.fname,cadet_record.lname,cadet_record.mname, student_id,
,MAX(case WHEN week = '02/18/2012' then present end) as day1
,MAX(case WHEN week = '02/19/2012' then present end) as day2
From attendance
LEFT JOIN cadet_record ON cadet_record.stud_no = attendance.student_id WHERE section = '$section' AND schoolyear = '$year' AND component = '$component' AND semester = '$semester'

GROUP BY student_id

Notice I added days instead of weeks because your example showed increasing days, although the column name was weeks

Answer 2

Without pivoting the table, you can get the weekly attendance of each student with this query:

SELECT 
    cadet_record.fname,
    cadet_record.lname,
    cadet_record.mname, 
    student_id,
    week,
    SUM(present) AS att
FROM attendance
LEFT JOIN cadet_record 
    ON cadet_record.stud_no = attendance.student_id 
WHERE section = '$section' 
    AND schoolyear = '$year' 
    AND component = '$component' 
    AND semester = '$semester'
GROUP BY week, student_id
ORDER BY week, cadet_record.fname, student_id

( EDIT Sorry, you should use SUM , not COUNT ).