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From 7d47517d579601bb6e59e33bf0896f0ed36aa0aa Mon Sep 17 00:00:00 2001
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From: Ondrej Dubaj <odubaj@redhat.com>
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Date: Mon, 20 Jan 2020 09:34:41 +0100
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Subject: [PATCH] Continue to back away from the LEFT JOIN optimization of
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check-in
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by disallowing query flattening if the outer query is DISTINCT. Without this fix,
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if an index scan is run on the table within the view on the right-hand side of the
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LEFT JOIN, stale result registers might be accessed yielding incorrect results,
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and/or an OP_IfNullRow opcode might be invoked on the un-opened table, resulting
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in a NULL-pointer dereference. This problem was found by the Yongheng and Rui fuzzer.
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---
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src/select.c | 8 ++++++--
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test/join.test | 13 +++++++++++++
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2 files changed, 19 insertions(+), 2 deletions(-)
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diff --git a/src/select.c b/src/select.c
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index c60ff27..0205a08 100644
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--- a/src/select.c
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+++ b/src/select.c
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@@ -3569,6 +3569,7 @@ static void substSelect(
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** (3b) the FROM clause of the subquery may not contain a virtual
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** table and
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** (3c) the outer query may not be an aggregate.
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+** (3d) the outer query may not be DISTINCT.
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**
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** (4) The subquery can not be DISTINCT.
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**
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@@ -3765,8 +3766,11 @@ static int flattenSubquery(
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*/
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if( (pSubitem->fg.jointype & JT_OUTER)!=0 ){
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isLeftJoin = 1;
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- if( pSubSrc->nSrc>1 || isAgg || IsVirtual(pSubSrc->a[0].pTab) ){
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- /* (3a) (3c) (3b) */
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+ if( pSubSrc->nSrc>1 /* (3a) */
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+ || isAgg /* (3b) */
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+ || IsVirtual(pSubSrc->a[0].pTab) /* (3c) */
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+ || (p->selFlags & SF_Distinct)!=0 /* (3d) */
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+ ){
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return 0;
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}
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}
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diff --git a/test/join.test b/test/join.test
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index 8c6f463..8c6a53d 100644
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--- a/test/join.test
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+++ b/test/join.test
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@@ -844,4 +844,17 @@ do_execsql_test join-15.110 {
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ORDER BY a1, a2, a3, a4, a5;
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} {1 {} {} {} {} 1 11 {} {} {} 1 12 {} {} {} 1 12 121 {} {} 1 13 {} {} {}}
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+# 2019-12-18 problem with a LEFT JOIN where the RHS is a view.
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+# Detected by Yongheng and Rui.
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+# Follows from the optimization attempt of check-in 41c27bc0ff1d3135
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+# on 2017-04-18
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+#
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+reset_db
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+do_execsql_test join-22.10 {
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+ CREATE TABLE t0(a, b);
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+ CREATE INDEX t0a ON t0(a);
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+ INSERT INTO t0 VALUES(10,10),(10,11),(10,12);
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+ SELECT DISTINCT c FROM t0 LEFT JOIN (SELECT a+1 AS c FROM t0) ORDER BY c ;
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+} {11}
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+
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finish_test
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--
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2.19.1
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