florian.schoppm...@emc.com (Florian Schoppmann) writes: > In PostgreSQL 9.1 and 9.2 (possibly also in earlier versions), the query
> --8<-- > WITH source AS ( > SELECT i FROM generate_series(1,10) AS i > ) > SELECT > i > FROM > source, ( > SELECT > count(*) AS _n > FROM source > ) AS _stats > WHERE > random() < 5::DOUBLE PRECISION/_n; > -->8-- [ doesn't do what you think it should ] I can't get excited about this. Any time you put a volatile function into WHERE, you're playing with fire. The docs warn against it: http://www.postgresql.org/docs/9.2/static/sql-expressions.html#SYNTAX-EXPRESS-EVAL To do what you want, I'd suggest wrapping the join into a sub-select with an "OFFSET 0" clause, which will serve as an optimization fence that prevents the random() call from being pushed down. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
