Hi I'm using cross join lateral with a non-trivial function in an attempt to limit calculation of that function, and am wondering about some aspects of how lateral is currently implemented. NB these queries are generated by a certain ORM, and are usually embedded in much more complex queries... Case one: counting select count(alpha.id) from alpha cross join lateral some_function(alpha.id) as some_val where alpha.test Here the function is strict, and moreover its argument will never be null - hence there should always be a non-null value returned. I would expect that since the function doesn't impact on the number of rows (always one value returned for each row in alpha), then I'd hope the function is never called. EXPLAIN shows it being called for each row in the main table. Case two: pagination select alpha.*, some_val from alpha cross join lateral some_function(alpha.id) as some_val where alpha.test order by alpha.name asc limit 100 offset 100 Same setup as above, and I'd expect that the ordering and selection of rows can be done first and the function only called on the rows that get selected. Again, EXPLAIN shows otherwise. So: am I expecting too much for LATERAL, or have I missed a trick somewhere? Many thanks in advance! Paul -- View this message in context: http://postgresql.nabble.com/query-laziness-of-lateral-join-with-function-tp5837706.html Sent from the PostgreSQL - performance mailing list archive at Nabble.com. -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
