From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Fri, 17 Sep 2004 18:29:24 +0000 (+0000)
Subject: Hashed LEFT JOIN would miss outer tuples with no inner match if the join
X-Git-Url: http://git.postgresql.org/gitweb/static/gitweb.js?a=commitdiff_plain;h=9ca9c6f4aa9135422f9a7b28d8c0db5b7be83ffa;p=users%2Fbernd%2Fpostgres.git

Hashed LEFT JOIN would miss outer tuples with no inner match if the join
was large enough to be batched and the tuples fell into a batch where
there were no inner tuples at all.  Thanks to Xiaoyu Wang for finding a
test case that exposed this long-standing bug.
---

diff --git a/src/backend/executor/nodeHashjoin.c b/src/backend/executor/nodeHashjoin.c
index 5b2b080b05..5c492f9743 100644
--- a/src/backend/executor/nodeHashjoin.c
+++ b/src/backend/executor/nodeHashjoin.c
@@ -568,12 +568,14 @@ ExecHashJoinNewBatch(HashJoinState *hjstate)
 	}
 
 	/*
-	 * We can skip over any batches that are empty on either side. Release
-	 * associated temp files right away.
+	 * Normally we can skip over any batches that are empty on either side
+	 * --- but for JOIN_LEFT, can only skip when left side is empty.
+	 * Release associated temp files right away.
 	 */
 	while (newbatch <= nbatch &&
-		   (innerBatchSize[newbatch - 1] == 0L ||
-			outerBatchSize[newbatch - 1] == 0L))
+		   (outerBatchSize[newbatch - 1] == 0L ||
+			(innerBatchSize[newbatch - 1] == 0L &&
+			 hjstate->js.jointype != JOIN_LEFT)))
 	{
 		BufFileClose(hashtable->innerBatchFile[newbatch - 1]);
 		hashtable->innerBatchFile[newbatch - 1] = NULL;