倒数mysql数据库中的字段值

Question

I have a field that hold integer for number of day.the number of this field is Between 1-6 .i want to make count down this field after a day.for example if the value of this field is 4 after one day the value of this field must change to 3 and after two day value of this field must change to 2.and when 4 day is over this field must delete . What should I do?

Answer 1

An alternative approach is to store the date when the field was first set and the count. Then you can get the count on any particular day using a view:

select t.*,
       greatest(0, cnt - datediff(date(now()), SetDate))) as currentvalue
from table t
having currentvalue > 0;

You don't actually have to delete the value from the table. It might be useful in the future for auditing purposes (unless the table is big, so reducing the size is actually useful).

Answer 2

you can do this by three ways as ,

1.Mysql Event scheduler 2.Cronjob 3.jquery setInterval()

But the best way to do is cornjob because, for event scheduler you need mysql server connection always open.And jquery setinterval() function will be called only when you refresh or loads the page were the setinterval() is called.

Answer 3

使用cron作业计划此脚本。

UPDATE table SET day = (day - 1) WHERE your condition;

Answer 4

Doesn't sound like a very sensible way to approach this. I assume you want to have, for example, a record that is automatically deleted after a while. Why don't you add a timestamp at which it expires? You can then either setup a scheduled job, as suggested by the commenters, or just run a query to DELETE FROM ... WHERE expiration_timestamp <= NOW() - for example - when the PHP script runs. This does not guarantee it gets run at most / at least once every day, but it does guarantee that the data is up to date when you access it.