When we pass an out-of-range value in UNIX_TIMESTAMP, MySQL returns 0. The valid range of value is same as for the TIMESTAMP data type.
Example
mysql> Select UNIX_TIMESTAMP('1969-01-01 04:05:45'); +---------------------------------------+ | UNIX_TIMESTAMP('1969-01-01 04:05:45') | +---------------------------------------+ | 0 | +---------------------------------------+ 1 row in set (0.00 sec)
When we pass an out-of-range value in FROM_UNIXTIME, MySQL returns NULL. The valid range of values is same as for the INTEGER data type.
Example
mysql> Select FROM_UNIXTIME(2147483648); +---------------------------+ | FROM_UNIXTIME(2147483648) | +---------------------------+ | NULL | +---------------------------+ 1 row in set (0.00 sec)