From 0e20abdb47e3499353ac4fd1b2d21e82ec6b1461 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Mon, 9 Apr 2012 11:58:24 -0400 Subject: [PATCH] Fix an Assert that turns out to be reachable after all. estimate_num_groups() gets unhappy with create table empty(); select * from empty except select * from empty e2; I can't see any actual use-case for such a query (and the table is illegal per SQL spec), but it seems like a good idea that it not cause an assert failure. --- src/backend/utils/adt/selfuncs.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c index 55e42025c6b..d700b86b934 100644 --- a/src/backend/utils/adt/selfuncs.c +++ b/src/backend/utils/adt/selfuncs.c @@ -3068,8 +3068,13 @@ estimate_num_groups(PlannerInfo *root, List *groupExprs, double input_rows) double numdistinct; ListCell *l; - /* We should not be called unless query has GROUP BY (or DISTINCT) */ - Assert(groupExprs != NIL); + /* + * If no grouping columns, there's exactly one group. (This can't happen + * for normal cases with GROUP BY or DISTINCT, but it is possible for + * corner cases with set operations.) + */ + if (groupExprs == NIL) + return 1.0; /* * Count groups derived from boolean grouping expressions. For other