[SQL] Getting the week of a date

[Kumar]

Dear Friends,   Postgres 7.3.4 on RH Linux7.2.   While this works for month and why not for week test=# select date_trunc('month',current_date + ('5 month')::INTERVAL);      date_trunc ---------------------  2004-07-01 00:00:00 (1 row)   test=# select date_trunc('week',current_date + ('5 month')::INTERVAL); ERROR:  TIMESTAMP units 'week' not supported test=#   Any idea on how to find the 3 rd Wednesday of any given month.   Thanks Kumar