MySQL SELECT WHERE datetime matches day (and not necessarily time)

Question

I have a table which contains a datetime column. I wish to return all records of a given day regardless of the time. Or in other words, if my table only contained the following 4 records, then only the 2nd and 3rd would be returned if I limit to 2012-12-25.

2012-12-24 00:00:00 2012-12-25 00:00:00 2012-12-25 06:00:00 2012-12-26 05:00:00 

Answer 1

NEVER EVER use a selector like DATE(datecolumns) = '2012-12-24' - it is a performance killer:

• it will calculate DATE() for all rows, including those, that don't match
• it will make it impossible to use an index for the query

It is much faster to use

SELECT * FROM tablename  WHERE columname BETWEEN '2012-12-25 00:00:00' AND '2012-12-25 23:59:59' 

as this will allow index use without calculation.

EDIT

As pointed out by Used_By_Already, in the time since the inital answer in 2012, there have emerged versions of MySQL, where using '23:59:59' as a day end is no longer safe. An updated version should read

SELECT * FROM tablename  WHERE columname >='2012-12-25 00:00:00' AND columname <'2012-12-26 00:00:00' 

The gist of the answer, i.e. the avoidance of a selector on a calculated expression, of course still stands.

Answer 2

... WHERE date_column >='2012-12-25' AND date_column <'2012-12-26' may potentially work better(if you have an index on date_column) than DATE.