Diogo Biazus <diogo(at)ikono(dot)com(dot)br> writes:
> I was wondering if postgres executes a subquery in an UPDATE clause once
> and use the result (of the subquery) for all the updates.
It should if the subquery is not dependent on any variables of the outer
table. To tell, run EXPLAIN on the query and look to see if you see
"InitPlan" (done once) or "SubPlan" (done each time result is needed).
regards, tom lane