From 0f9efd54ceb0e2b42841f5eb15d30072d210bac2 Mon Sep 17 00:00:00 2001
From: Igor Babaev <igor@askmonty.org>
Date: Fri, 3 Aug 2018 23:27:24 -0700
Subject: [PATCH] MDEV-16359 wrong result (extra rows) on the query with UNION
 and brackets

Due to an obvious bug in st_select_lex_unit::reset_distinct() a union
without duplicates of more than 2 selects could return a result set
containing duplicate rows if this union was enclosed in ().
---
 mysql-test/main/brackets.result | 12 ++++++++++++
 mysql-test/main/brackets.test   |  8 ++++++++
 sql/sql_lex.cc                  |  1 -
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/mysql-test/main/brackets.result b/mysql-test/main/brackets.result
index 194807290a0..479b74b69e4 100644
--- a/mysql-test/main/brackets.result
+++ b/mysql-test/main/brackets.result
@@ -207,4 +207,16 @@ a	b
 1	100
 3	30
 drop table t1;
+#
+# MDEV-16359: union with 3 selects in brackets
+#
+select 1 union select 1 union select 1;
+1
+1
+(select 1 union select 1 union select 1);
+1
+1
+((select 1) union (select 1) union (select 1));
+1
+1
 # End of 10.4 tests
diff --git a/mysql-test/main/brackets.test b/mysql-test/main/brackets.test
index ac22770ffc2..699c70a900f 100644
--- a/mysql-test/main/brackets.test
+++ b/mysql-test/main/brackets.test
@@ -80,5 +80,13 @@ select a,b from t1 order by 1 limit 3;
 
 drop table t1;
 
+--echo #
+--echo # MDEV-16359: union with 3 selects in brackets
+--echo #
+
+select 1 union select 1 union select 1;
+(select 1 union select 1 union select 1);
+((select 1) union (select 1) union (select 1));
+
 --echo # End of 10.4 tests
 
diff --git a/sql/sql_lex.cc b/sql/sql_lex.cc
index fa8155507f8..20b1eb413cf 100644
--- a/sql/sql_lex.cc
+++ b/sql/sql_lex.cc
@@ -8763,7 +8763,6 @@ void st_select_lex_unit::reset_distinct()
     if (sl->distinct)
     {
       union_distinct= sl;
-      return;
     }
   }
 }