>>>>> "David" == David Fetter <da...@fetter.org> writes:
>> Consider the difference between (in the absence of CTE inlining): >> >> -- inline subquery with no optimization barrier (qual may be pushed down) >> select * from (select x from y) s where x=1; David> ...and doesn't need to materialize all of y, >> -- inline subquery with optimization barrier (qual not pushed down) >> select * from (select x from y offset 0) s where x=1; >> >> -- CTE with materialization >> with s as (select x from y) select * from s where x=1; David> while both of these do. The non-CTE one has to _evaluate_ the whole of the "s" subquery, but it doesn't have to actually store the result, whereas the CTE version needs to put it all in a tuplestore and read it back. -- Andrew (irc:RhodiumToad)
