unix_timestamp()
mysql> select unix_timestamp();
+------------------+
| unix_timestamp() |
+------------------+
| 1464590043 |
+------------------+
unix_timestamp(date)
mysql> select unix_timestamp('2016-05-30');
+------------------------------+
| unix_timestamp('2016-05-30') |
+------------------------------+
| 1464537600 |
+------------------------------+
mysql> select unix_timestamp('2016-05-30 14:35:21');
+---------------------------------------+
| unix_timestamp('2016-05-30 14:35:21') |
+---------------------------------------+
| 1464590121 |
+---------------------------------------+
from_unixtime(unix_timestamp)
mysql> select from_unixtime(1464590043);
+---------------------------+
| from_unixtime(1464590043) |
+---------------------------+
| 2016-05-30 14:34:03 |
+---------------------------+
from_unixtime(unix_timestamp,format)
mysql> select from_unixtime(1464590043, '%Y %D %M %h:%i:%s %x');
+---------------------------------------------------+
| from_unixtime(1464590043, '%Y %D %M %h:%i:%s %x') |
+---------------------------------------------------+
| 2016 30th May 02:34:03 2016 |
+---------------------------------------------------+