UNIX_TIMESTAMP()
Should do the trick!
From MySQL Docs:
If called with no argument, returns a Unix timestamp (seconds since
'1970-01-01 00:00:00' UTC) as an unsigned integer. If UNIX_TIMESTAMP()
is called with a date argument, it returns the value of the argument
as seconds since '1970-01-01 00:00:00' UTC. date may be a DATE string,
a DATETIME string, a TIMESTAMP, or a number in the format YYMMDD or
YYYYMMDD. The server interprets date as a value in the current time
zone and converts it to an internal value in UTC.
mysql> SELECT UNIX_TIMESTAMP();
-> 1196440210
mysql> SELECT UNIX_TIMESTAMP('2007-11-30 10:30:19');
-> 1196440219