Porting from mysql to psql (UNIX_TIMESTAMP()?)

Hi!

As subject says, we are currently porting all of our data, programs
and logic from mysql to postgresql. One of the things we have yet to
resolve is how to replace mysql's UNIX_TIMESTAMP() function we used
extensively in PosgreSQL?

Function works like this in mysql:

mysql> select start from connection limit 1;
+---------------------+
| start               |
+---------------------+
| 2000-07-03 20:12:37 |
+---------------------+
1 row in set (0.01 sec)

mysql> select UNIX_TIMESTAMP(start) from connection limit 1;
+-----------------------+
| UNIX_TIMESTAMP(start) |
+-----------------------+
|             962647957 |
+-----------------------+
1 row in set (0.00 sec)

Is there any similar functionality (returning unixish number of
seconds since 1970 from the timestamp field) in PostgreSQL?

I tried all of the available date/time functions, type casting but all
to no avail.

TIA,
--
Zlatko

P.S Is it bad manners crossposting to two pgsql mailing list? Still
new to PostgreSQL, still learning...