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 |
Since the seconds are from 0 (1970-01-01 00:00:00 UTC
), you should look for every multiple of 60
SELECT * FROM mytable WHERE MOD(TimeStamp,60)=0;
or if TimeStamp is indexed, you can do
SELECT T.* FROM
(SELECT TimeStamp FROM mytable WHERE MOD(TimeStamp,60)=0) M
INNER JOIN mytable T USING (TimeStamp);
Give it a Try !!!
SUGGESTION #1
You should store the timestamp of the minute and index it
ALTER TABLE mytable ADD COLUMN MinuteTimeStamp AFTER TimeStamp;
UPDATE mytable SET MinuteTimeStamp = TimeStamp - MOD(TimeStamp,60);
ALTER TABLE mytable ADD INDEX MinuteTimeStamp_UniqueKey_ndx (MinuteTimeStamp,UniqueKey);
Then, you can do MIN aggregation on MinuteTimeStamp.
SELECT MinuteTimeStamp,MIN(UniqueKey) UniqueKey
FROM mytable GROUP BY MinuteTimeStamp;
and use it get those records
SELECT B.* FROM
(SELECT MinuteTimeStamp,MIN(UniqueKey) UniqueKey
FROM mytable GROUP BY MinuteTimeStamp) A
INNER JOIN mytable B USING (UniqueKey);
It was tactfully pointed out that triggers would degrade performance
Perhaps doing INSERTs like this may help
INSERT INTO mytable (UniqueKey,TimeStamp,MinuteTimeStamp) VALUES
(
uniquevalue,
UNIX_TIMESTAMP(NOW()),
UNIX_TIMESTAMP(NOW() - INTERVAL SECOND(NOW()) SECOND)
);
SUGGESTION #2
Since you have over 1000 columns (Ugh), perhaps a table of those minute timestamps would be better.
CREATE TABLE MinuteKeys
(
MinuteTimeStamp INT UNSIGNED NOT NULL,
UniqueKey INT UNSIGNED NOT NULL,
PRIMARY KEY (UniqueKey)
KEY MinuteTimeStamp_UniqueKey_ndx (MinuteTimeStamp,UniqueKey)
) ENGINE=MyISAM;
ALTER TABLE MinuteKeys DISABLE KEYS;
INSERT INTO MinuteKeys SELECT TimeStamp - MOD(TimeStamp,60),UniqueKey FROM mytable;
ALTER TABLE MinuteKeys ENABLE KEYS;
Then, you could use that table for the aggregation
SELECT B.* FROM
(SELECT MinuteTimeStamp,MIN(UniqueKey) UniqueKey
FROM MinuteKeys GROUP BY MinuteTimeStamp) A
INNER JOIN mytable B USING (UniqueKey);
EPILOGUE
Other suggestions are possible but you should really consider normalization of the table
See my post Too many columns in MySQL as to why
Best Answer
If you were able to start with a new table I would use this structure to store the data:
This way you can store data for any time period and work out the days needed from the date.
Since you can't create that we'll have to see if we can modify what you've got in a query. I've had a play and this will get the data into a table format that I believe would be easier to work with:
You'll have to add as many
union all
elements as you have columns but then you can filter on the number of days you want. You will now be able toGROUP BY
and perform any calculations you need to.For keeping your main queries cleaner and smaller I'd recommend creating a
VIEW
for the subquery with all of theUNION ALL
statements in.