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Avoid division by zero in estimate_num_groups() when table has no rows.

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This commit is contained in:
Tom Lane
2003-10-16 21:37:54 +00:00
parent 624292aa35
commit 64c1fc7257
1 changed files with 15 additions and 9 deletions
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24
src/backend/utils/adt/selfuncs.c
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@ -15,7 +15,7 @@
* *
* *
* IDENTIFICATION * IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/utils/adt/selfuncs.c,v 1.146 2003/09/25 06:58:04 petere Exp $ * $Header: /cvsroot/pgsql/src/backend/utils/adt/selfuncs.c,v 1.147 2003/10/16 21:37:54 tgl Exp $
* *
*------------------------------------------------------------------------- *-------------------------------------------------------------------------
*/ */
@ -2166,17 +2166,23 @@ estimate_num_groups(Query *root, List *groupExprs, double input_rows)
} }
/* /*
* Clamp to size of rel, multiply by restriction selectivity. * Sanity check --- don't divide by zero if empty relation.
*/ */
Assert(rel->reloptkind == RELOPT_BASEREL); Assert(rel->reloptkind == RELOPT_BASEREL);
if (reldistinct > rel->tuples) if (rel->tuples > 0)
reldistinct = rel->tuples; {
reldistinct *= rel->rows / rel->tuples; /*
* Clamp to size of rel, multiply by restriction selectivity.
*/
if (reldistinct > rel->tuples)
reldistinct = rel->tuples;
reldistinct *= rel->rows / rel->tuples;
/* /*
* Update estimate of total distinct groups. * Update estimate of total distinct groups.
*/ */
numdistinct *= reldistinct; numdistinct *= reldistinct;
}
varinfos = newvarinfos; varinfos = newvarinfos;
} while (varinfos != NIL); } while (varinfos != NIL);