Tom Lane <[EMAIL PROTECTED]> writes: > It's conceivable that the planner could prove that neither effect is > possible in a particular query and then make the transformation > automatically, but I'm not about to expend that kind of planning effort > on such an odd case --- checking for it would waste entirely too many > cycles in most cases.
Fwiw these aren't really very rare cases. Usually it goes the other direction though. I seem to recall Oracle did in fact support a plan where it converted OR expressions into a kind of union plan node. But I think Postgres's bitmap index scan satisfies much of the same need. I think the most useful case where the union plan was beneficial was precisely when you had something like WHERE index_col1=1 OR indexed_col2=2. Going from an UNION plan to a OR plan would be somewhat strange. Programmers don't usually write plans as UNION in place of the more natural OR unless they have a reason to. -- greg ---------------------------(end of broadcast)--------------------------- TIP 6: explain analyze is your friend
