mysql> select now(); +---------------------+ | now() | +---------------------+ | 2009-01-31 21:54:36 | +---------------------+ 1 row in set (0.00 sec)
mysql> select unix_timestamp(now()); +-----------------------+ | unix_timestamp(now()) | +-----------------------+ | 1233435200 | +-----------------------+ 1 row in set (0.00 sec)
mysql> select from_unixtime(1233435200); +---------------------------+ | from_unixtime(1233435200) | +---------------------------+ | 2009-01-31 21:53:20 | +---------------------------+ 1 row in set (0.00 sec)
mysql> select count(*) from sessions where timestamp > unix_timestamp(now() - interval 31 day); +----------+ | count(*) | +----------+ | 8711 | +----------+ 1 row in set (0.06 sec)
mysql> select count(*) from sessions where timestamp > unix_timestamp("2009-01-01 00:00:00") and timestamp < unix_timestamp("2009-01-31 00:00:00"); +----------+ | count(*) | +----------+ | 8407 | +----------+ 1 row in set (0.08 sec)
more info: http://dev.mysql.com/doc/refman/5.1/en/date-and-time-functions.html