Find difference between timestamps in seconds in PostgreSQL

Question

I have a table in PostgreSQL 8.3 with 2 timestamp columns. I would like to get the difference between these timestamps in seconds. Cou

Answer 1

select age(timestamp_A, timestamp_B)

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Answering to Igor's comment:

select age('2013-02-28 11:01:28'::timestamp, '2011-12-31 11:00'::timestamp);
              age              
-------------------------------
 1 year 1 mon 28 days 00:01:28

Answer 2

SELECT (cast(timestamp_1 as bigint) - cast(timestamp_2 as bigint)) FROM table;

In case if someone is having an issue using extract.

Answer 3

Try: 

SELECT EXTRACT(EPOCH FROM (timestamp_B - timestamp_A))
FROM TableA

Details here: EXTRACT.