From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sun, 17 Sep 2017 19:28:51 +0000 (-0400)
Subject: Allow rel_is_distinct_for() to look through RelabelType below OpExpr.
X-Git-Tag: REL9_5_10~53
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=eeff6839633d97c03a43889ed7c83df81d513f08;p=postgresql

Allow rel_is_distinct_for() to look through RelabelType below OpExpr.

This lets it do the right thing for, eg, varchar columns.
Back-patch to 9.5 where this logic appeared.

David Rowley, per report from Kim Rose Carlsen

Discussion: https://postgr.es/m/VI1PR05MB17091F9A9876528055D6A827C76D0@VI1PR05MB1709.eurprd05.prod.outlook.com
---

diff --git a/src/backend/optimizer/plan/analyzejoins.c b/src/backend/optimizer/plan/analyzejoins.c
index d188d9724a..9b4c1033c9 100644
--- a/src/backend/optimizer/plan/analyzejoins.c
+++ b/src/backend/optimizer/plan/analyzejoins.c
@@ -345,6 +345,14 @@ join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
 			else
 				var = (Var *) get_leftop(rinfo->clause);
 
+			/*
+			 * We may ignore any RelabelType node above the operand.  (There
+			 * won't be more than one, since eval_const_expressions() has been
+			 * applied already.)
+			 */
+			if (var && IsA(var, RelabelType))
+				var = (Var *) ((RelabelType *) var)->arg;
+
 			/*
 			 * If inner side isn't a Var referencing a subquery output column,
 			 * this clause doesn't help us.