Timestamp problem

Hai All,

I have been using Mysql in which I used unix_timestamp() function
to retrieve the time using the queries. As it gives time in seconds the life
is easy to store it in database and to compare with the other times. But now I
am moving to PostgreSQL in which there is a function current_timestamp to
retrieve time, but now it became hard for me to store it in database in the
string format and to compare it with other times again.

Is there any function in PostgreSQL which returns time in
seconds like unix_timestamp() in Mysql. Please suggest me some ways to get rid
of this problem.

My email: kumar(at)cc(dot)usu(dot)edu .
Thank you All,
Kumar.