I would go for the first option, mostly because I believe that less columns are better.
But also:
First of all, the first option would only require an insert when a student is absent, while the second would, first, have an insert for each student at each month, and then for each student that is absent, it would require to update the row each time the student is absent.
The second option would however give a good matrix directly in the database which days a student is absent, but that would be easily achieved through PHP.
Also, having one row per day a student is absent, allows for better statistics when it comes to reporting.
For instance, check how many students that were absent during one month:
select month(date), count(*) from attendance where is_absent = 1 group by month(date);
compared to (here I assume that d1..d31 is an integer with either 1 or 0)
select month(date), sum(d1+d2+d3+d4+d5..+d31) from attendance group by month(date);
Or, if you have a student
table as well (which I assume you will have) and you want to see which students were not absent:
select student_name
from students
where student_id not in (select student_id from attendance)
Compared to:
select student_name
from students s
join attendance a on s.student_id = a.student_id
where (d1+d2+d3+d4+d5..+d31) = 0
Finally, since you wanted to store the reason for the student to be absent, it means for option 2 you would either, have one more row for each reason or have one more column for each day which stores the reason, since otherwise you could only store one reason per month, unless you store the reason as a concatenated string in the column which would require a separator and thus limit the characters you put in as reason.
However, in the end it is more of a personal preference, since with correctly created indexes, I doubt that you would have to worry about the performance, but depending on the amount of absent students, option 2 would be using more storage than option 1 (number of columns * rows * size of the data types)
This type of rotation of data from columns to rows is known as a PIVOT. MySQL does not have a pivot function but you can use an aggregate function with a CASE expression to get the result.
My first suggestion would be to determine if you have a calendar
table or a table that contains all of the dates that you want to display. If not, then I would suggest creating one similar to the following:
CREATE TABLE calendar (`Date` datetime) ;
INSERT INTO calendar (`Date`)
VALUES
('2013-06-01 00:00:00'),
('2013-06-02 00:00:00'),
('2013-06-03 00:00:00'),
('2013-06-04 00:00:00'),
('2013-06-05 00:00:00'),
('2013-06-06 00:00:00'),
('2013-06-07 00:00:00'),
('2013-06-08 00:00:00'),
('2013-06-09 00:00:00'),
('2013-06-10 00:00:00');
This will make it possible for you to generate a list of all of the dates that you want to display.
Second, you will need to generate the list of each student and each date. You can do this by using a CROSS JOIN between your tbl_admission
and the calendar
table:
select c.date, a.studentname, a.rollno, a.class
from calendar c
cross join tbl_admission a;
See Demo. Once you have this list, then you can use a LEFT JOIN to your existing tbl_absentees
table to get the result:
select
ca.studentname,
ca.rollno,
ca.class,
max(case when ca.date = '2013-06-01' then coalesce(p.status, 'P') end) `2013-06-01`,
max(case when ca.date = '2013-06-02' then coalesce(p.status, 'P') end) `2013-06-02`,
max(case when ca.date = '2013-06-03' then coalesce(p.status, 'P') end) `2013-06-03`,
max(case when ca.date = '2013-06-04' then coalesce(p.status, 'P') end) `2013-06-04`,
max(case when ca.date = '2013-06-05' then coalesce(p.status, 'P') end) `2013-06-05`,
max(case when ca.date = '2013-06-06' then coalesce(p.status, 'P') end) `2013-06-06`,
max(case when ca.date = '2013-06-07' then coalesce(p.status, 'P') end) `2013-06-07`,
max(case when ca.date = '2013-06-08' then coalesce(p.status, 'P') end) `2013-06-08`,
max(case when ca.date = '2013-06-08' then coalesce(p.status, 'P') end) `2013-06-09`,
max(case when ca.date = '2013-06-10' then coalesce(p.status, 'P') end) `2013-06-10`
from
(
select c.date, a.studentname, a.rollno, a.class
from calendar c
cross join tbl_admission a
) ca
left join tbl_absentees p
on ca.rollno = p.rollno
and ca.date = p.date
group by ca.studentname, ca.rollno, ca.class
order by ca.rollno;
See SQL Fiddle with Demo. Of course for your request, you most likely want to query the data based on a date range so you will not want to hard-code the values. If that is the case, then you will need to look at using a prepared statement to generate dynamic SQL:
SET @sql = NULL;
SELECT
GROUP_CONCAT(DISTINCT
CONCAT(
'max(CASE WHEN ca.date = ''',
date_format(date, '%Y-%m-%d'),
''' THEN coalesce(p.status, ''P'') END) AS `',
date_format(date, '%Y-%m-%d'), '`'
)
) INTO @sql
FROM calendar
where date>='2013-06-01'
and date <= '2013-06-05';
SET @sql
= CONCAT('SELECT ca.studentname,
ca.rollno,
ca.class, ', @sql, '
from
(
select c.date, a.studentname, a.rollno, a.class
from calendar c
cross join tbl_admission a
) ca
left join tbl_absentees p
on ca.rollno = p.rollno
and ca.date = p.date
where ca.date>=''2013-06-01''
and ca.date <= ''2013-06-05''
group by ca.studentname, ca.rollno, ca.class
order by ca.rollno');
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
See SQL Fiddle with Demo. Both of these queries will give a result similar to:
| STUDENTNAME | ROLLNO | CLASS | 2013-06-01 | 2013-06-02 | 2013-06-03 | 2013-06-04 | 2013-06-05 | 2013-06-06 | 2013-06-07 | 2013-06-08 | 2013-06-09 | 2013-06-10 |
------------------------------------------------------------------------------------------------------------------------------------------------------------------
| Naren | 1 | 22 | A | A | A | A | P | P | P | P | P | P |
| Srinu | 2 | 22 | P | P | P | P | P | P | P | P | P | P |
| Blah | 3 | 22 | A | P | P | P | P | P | P | P | P | P |
Best Answer
To expand more on @Twinkles alternative, I'm concerned about why you're storing present and absent students in your attendance data. Is it because you want to be able to run a report that shows all kids and whether they were absent on a given day? There's a better way to do it.
Most systems I've seen store either the that the student is present (Positive attendance) or the student is absent (Negative attendance, although rarely referred to by that name). The decision on which to use came down to the structure and reporting requirements of the school (and whoever they report to).
If you're school is concerned when the student is absent for reasons like having to track Truant students, you should use a standard (negative) attendance structure. Most K-12 schools in the US do it this way.
If you're school only awards credit for courses after a verified number of hours have been completed (e.g. Johnny doesn't pass the course until he's completed his coursework and attended 12 sessions of the class), then a positive attendance structure could be used.
Assuming your data looked like this: (Ignoring the course_id in your example for simplicity)
To get a report of all the kids at your school and their attendance status for the day, you could run a query like:
Which would return: