Select 对应一个时间的所有行

Question

I have a script that sends out emails every minute. When it starts its loop, it queries the database for all entries that are equal to the current utc time. I would like to have it find all entries in the database that correspond to the current time down to the minute.

So there is a 'time' column that stores the utc time: '2009-03-06 20:18:31'. When it searches is there any way to ignore the seconds attribute with out changing how I store the time?

EDIT: I'm using mysql server.

Thanks!

Answer 1

In MySQL :

SELECT *
FROM   table
WHERE  time >= NOW() - INTERVAL EXTRACT(SECOND FROM NOW()) SECOND
       AND time < NOW() - INTERVAL (EXTRACT(SECOND FROM NOW()) + 60) SECOND

This will efficiently use an index on time field.

Answer 2

I've performed this logic before:

Query for: TimeField >= (Now - 1 Minute).

You could also modify this logic to query for TimeField >= (Now - # of seconds passed in the current minute) - this might more accurately retrieve what you are looking for.

Answer 3

Make sure you do the calculation on the "now" part of the inequality. In SQL Server you can use DATEADD(mi, -1, GETDATE()). If you perform the function on the column, you'll likely end up generating a RBAR operation.

Answer 4

where datediff(minute, Time, getdate()) = 0

This will work on SQL Server, but as you don't specify what server you're using it's hard to tell if it will work for you.

Answer 5

this was the actual sql statement that I used. Notice that it was heavy influenced by Quassnoi's response but there are some key differences. I used the UTC_TIMESTAMP instead of NOW().

select * 
from table
where time < UTC_TIMESTAMP() + INTERVAL(1) MINUTE  - INTERVAL (EXTRACT(SECOND FROM UTC_TIMESTAMP())) SECOND 
and time >= UTC_TIMESTAMP() - INTERVAL (EXTRACT(SECOND FROM UTC_TIMESTAMP())) SECOND;