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Fix an Assert that turns out to be reachable after all.

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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.
This commit is contained in:
Tom Lane 2012-04-09 11:58:24 -04:00
parent 785d4998b6
commit be9aad6b9e
1 changed files with 7 additions and 2 deletions
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9
src/backend/utils/adt/selfuncs.c
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@ -3051,8 +3051,13 @@ 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