From bbf4fdc2538097bb3103806e1419ceef1f289203 Mon Sep 17 00:00:00 2001
From: Neil Conway <neilc@samurai.com>
Date: Wed, 19 Sep 2007 22:31:48 +0000
Subject: [PATCH] Prevent corr() from returning the wrong results for negative
 correlation values. The previous coding essentially assumed that x =
 sqrt(x*x), which does not hold for x < 0.

Thanks to Jie Zhang at Greenplum and Gavin Sherry for reporting this
issue.
---
 src/backend/utils/adt/float.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/src/backend/utils/adt/float.c b/src/backend/utils/adt/float.c
index 7a66bd4c56..53bfd321d7 100644
--- a/src/backend/utils/adt/float.c
+++ b/src/backend/utils/adt/float.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/float.c,v 1.150 2007/06/05 21:31:06 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/float.c,v 1.151 2007/09/19 22:31:48 neilc Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2274,8 +2274,7 @@ float8_corr(PG_FUNCTION_ARGS)
 	if (numeratorX <= 0 || numeratorY <= 0)
 		PG_RETURN_NULL();
 
-	PG_RETURN_FLOAT8(sqrt((numeratorXY * numeratorXY) /
-						  (numeratorX * numeratorY)));
+	PG_RETURN_FLOAT8(numeratorXY / sqrt(numeratorX * numeratorY));
 }
 
 Datum
-- 
2.40.0