SAMPLE 1000 OF (SELECT * FROM mydata WHERE <some condition>)should return 1000 random rows from the select statement so that two consecutive evaluations of the query would only with very little probability return the same 1000 rows.
(Yes, I know that "SAMPLE 1000 OF" is not valid SQL) ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster