time calculation

Dear sirs:

Please I need to solve this problem:

I need to sustract two values timestamp type and return the
difference in seconds, exists some funciton on postgresql for
do this?

e.g:

I have value1='2001-10-01 12:50:13' and value2='2001-09-10
12:53:10'

I need to calculate value1-value2 and return how many seconds
there are between both timestamps.

thank you

Ernesto

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