On 15/07/10 17:55, Alban Hertroys wrote: > On 15 Jul 2010, at 3:05, Craig Ringer wrote: > >> It was an example of how it'd be nice to avoid the need for a join when >> dealing with scalar values. I'd love to be able to write: >> >> WITH aconstant AS (1) >> SELECT x.*, aconstant FROM generate_series(1,10) AS x; >> >> ... but can't presently do so because the WITH terms are only visible as >> potential from-list items. > > > But why is that a problem? The below seems to work just fine: > > dalroi=> WITH constants AS (SELECT 1 AS aconstant) > SELECT 'x' AS column, aconstant FROM constants WHERE aconstant = 1; > column | aconstant > --------+----------- > x | 1 > (1 row) > > Sure, you'll have to join with the with-query to get any meaningful results, > but if there are any complicated calculations in that query, won't they be > calculated just once - like you intended? > > If not, I think we're all failing to see the point you're trying to make.
The join its self is expensive. See the plans I posted in the post you're replying to. -- Craig Ringer -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
