MYSQL Date Time Round To Nearest Hour

Question

I have a date time field in a MySQL database and wish to output the result to the nearest hour.

e.g. 2012-04-01 00:00:01 should read 2012-04-01 00

Answer 1

soul's first solution truncates instead of rounding and the second solution doesn't work with Daylight Savings cases such as:

select FROM_UNIXTIME(UNIX_TIMESTAMP('2012-03-11 2:14:00') - MOD(UNIX_TIMESTAMP('2012-03-11 2:14:00'),300));

Here is an alternate method (1):

DATE_ADD(
    tick,
    INTERVAL (IF((MINUTE(tick)*60)+SECOND(tick) < 1800, 0, 3600) - (MINUTE(tick)*60)+SECOND(tick)) SECOND
)

If you don't need to worry about seconds you can simplify it like this (2):

DATE_ADD(
    tick,
    INTERVAL (IF(MINUTE(tick) < 30, 0, 60) - MINUTE(tick)) MINUTE
)

Or if you prefer to truncate instead of round, here is simpler version of soul's method (3):

DATE_SUB(tick, INTERVAL MINUTE(tick)*60+SECOND(tick) SECOND)

EDIT: I profiled some of these queries on my local machine and found that for 100,000 rows the average times were as follows:

• soul's UNIXTIME method: 0.0423 ms (fast, but doesn't work with DST)
• My method 3: 0.1255 ms
• My method 2: 0.1289 ms
• Ben Lee's DATE_FORMAT method: 0.1495 ms
• My method 1: 0.1506 ms