From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu, 16 Oct 2003 21:37:54 +0000 (+0000)
Subject: Avoid division by zero in estimate_num_groups() when table has no rows.
X-Git-Url: http://git.postgresql.org/gitweb/static/gitweb.js?a=commitdiff_plain;h=54bd29c29cf0e88a41267c77f1153df2acf81f00;p=users%2Fbernd%2Fpostgres.git

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

diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index d4297d4d74..6a06866156 100644
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -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);
-		if (reldistinct > rel->tuples)
-			reldistinct = rel->tuples;
-		reldistinct *= rel->rows / rel->tuples;
+		if (rel->tuples > 0)
+		{
+			/*
+			 * 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.
-		 */
-		numdistinct *= reldistinct;
+			/*
+			 * Update estimate of total distinct groups.
+			 */
+			numdistinct *= reldistinct;
+		}
 
 		varinfos = newvarinfos;
 	} while (varinfos != NIL);