Disallow extended statistics on system columns

tvondra · tvondra · commit 66061077155d · 2021-09-20T00:45:29.000+02:00
Since introduction of extended statistics, we've disallowed references to system columns. So for example CREATE STATISTICS s ON ctid FROM t; would fail. But with extended statistics on expressions, it was possible to work around this limitation quite easily CREATE STATISTICS s ON (ctid::text) FROM t; This is an oversight in a4d75c8, fixed by adding a simple check. Backpatch to PostgreSQL 14, where support for extended statistics on expressions was introduced. Backpatch-through: 14 Discussion: https://postgr.es/m/20210816013255.GS10479%40telsasoft.com
diff --git a/src/backend/commands/statscmds.c b/src/backend/commands/statscmds.c
@@ -287,9 +287,24 @@ CreateStatistics(CreateStatsStmt *stmt)
 			Node	   *expr = selem->expr;
 			Oid			atttype;
 			TypeCacheEntry *type;
+			Bitmapset  *attnums = NULL;
+			int			k;
 
 			Assert(expr != NULL);
 
+			/* Disallow expressions referencing system attributes. */
+			pull_varattnos(expr, 1, &attnums);
+
+			k = -1;
+			while ((k = bms_next_member(attnums, k)) >= 0)
+			{
+				AttrNumber	attnum = k + FirstLowInvalidHeapAttributeNumber;
+				if (attnum <= 0)
+					ereport(ERROR,
+						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+						 errmsg("statistics creation on system columns is not supported")));
+			}
+
 			/*
 			 * Disallow data types without a less-than operator.
 			 *
