Question

How can I update a table after some time interval when a condtion is matched?

tb_contest
id   contest_id   name   is_expire
1    101          new    0
2    102          old    0

tb_answer
contest_id   answer_id   date
101          1           2012-02-02
101          2           2012-09-14
102          5           2012-06-01

I need to update tb_contest after some condition was met and make is_expire=1 after 2 days on basis of the last answer received i:e 2012-03-14, so the tb_contest should be updated on 2012-09-16.

Answer 1

Try this one,

UPDATE tb_contest a INNER JOIN
        (
            SELECT contest_ID, MAX(`date`) maxDate
            FROM tb_answer
            GROUP BY contest_ID
        ) b ON a.contest_ID = b.contest_ID
SET a.is_expire = 1
WHERE   DATEDIFF(CURDATE(), b.maxDate) >= 2 AND 
        a.is_expire = 0

So here it goes, the two tables were joined by contest_ID and having the lastest answered date on tb_answer. By using DATEDIFF() we can know the difference between today’s date and the date the contest has been answered.