Bug#47371 reference by same column name

At the end of execution top level join execution
we cleanup this join with true argument.
It leads to underlying join cleanup(subquery) with true argument too
and to tmp_table_param->field array cleanup which is required later.
The problem is that Item_func_set_user_var does not set
result_filed which leads to unnecessary repeated excution of subquery
on final stage.
The fix is to set result_field for Item_func_set_user_var.

mysql-test/r/count_distinct.result

@@ -40,6 +40,26 @@ select t2.isbn,city,t1.libname,count(distinct t1.libname) as a from t3 left join
 isbn	city	libname	a
 007	Berkeley	Berkeley Public1	2
 000	New York	New York Public Libra	2
+select t2.isbn,city,@bar:=t1.libname,count(distinct t1.libname) as a
+from t3 left join t1 on t3.libname=t1.libname left join t2
+on t3.isbn=t2.isbn group by city having count(distinct
+t1.libname) > 1;
+isbn	city	@bar:=t1.libname	a
+007	Berkeley	Berkeley Public1	2
+000	New York	New York Public Libra	2
+SELECT @bar;
+@bar
+Berkeley Public2
+select t2.isbn,city,concat(@bar:=t1.libname),count(distinct t1.libname) as a
+from t3 left join t1 on t3.libname=t1.libname left join t2
+on t3.isbn=t2.isbn group by city having count(distinct
+t1.libname) > 1;
+isbn	city	concat(@bar:=t1.libname)	a
+007	Berkeley	Berkeley Public1	2
+000	New York	New York Public Libra	2
+SELECT @bar;
+@bar
+Berkeley Public2
 drop table t1, t2, t3;
 create table t1 (f1 int);
 insert into t1 values (1);

mysql-test/r/user_var.result

@@ -363,4 +363,19 @@ SELECT a, b FROM t1 WHERE a=2 AND b=3 GROUP BY a, b;
 a	b
 2	3
 DROP TABLE t1;
+CREATE TABLE t1 (f1 int(11) default NULL, f2 int(11) default NULL);
+CREATE TABLE t2 (f1 int(11) default NULL, f2 int(11) default NULL, foo int(11));
+CREATE TABLE t3 (f1 int(11) default NULL, f2 int(11) default NULL);
+INSERT INTO t1 VALUES(10, 10);
+INSERT INTO t1 VALUES(10, 10);
+INSERT INTO t2 VALUES(10, 10, 10);
+INSERT INTO t2 VALUES(10, 10, 10);
+INSERT INTO t3 VALUES(10, 10);
+INSERT INTO t3 VALUES(10, 10);
+SELECT MIN(t2.f1),
+@bar:= (SELECT MIN(t3.f2) FROM t3 WHERE t3.f2 > foo)
+FROM t1,t2 WHERE t1.f1 = t2.f1 ORDER BY t2.f1;
+MIN(t2.f1)	@bar:= (SELECT MIN(t3.f2) FROM t3 WHERE t3.f2 > foo)
+10	NULL
+DROP TABLE t1, t2, t3;
 End of 5.0 tests

mysql-test/t/count_distinct.test

@@ -35,6 +35,25 @@ insert into t1 values ('NYC Lib','New York');
 select t2.isbn,city,t1.libname,count(t1.libname) as a from t3 left join t1 on t3.libname=t1.libname left join t2 on t3.isbn=t2.isbn group by city,t1.libname;
 select t2.isbn,city,t1.libname,count(distinct t1.libname) as a from t3 left join t1 on t3.libname=t1.libname left join t2 on t3.isbn=t2.isbn group by city having count(distinct t1.libname) > 1;
 select t2.isbn,city,t1.libname,count(distinct t1.libname) as a from t3 left join t1 on t3.libname=t1.libname left join t2 on t3.isbn=t2.isbn group by city having count(distinct concat(t1.libname,'a')) > 1;
+
+select t2.isbn,city,@bar:=t1.libname,count(distinct t1.libname) as a
+       from t3 left join t1 on t3.libname=t1.libname left join t2
+       on t3.isbn=t2.isbn group by city having count(distinct
+       t1.libname) > 1;
+#
+# Wrong result, see bug#49872
+# 
+SELECT @bar;
+
+select t2.isbn,city,concat(@bar:=t1.libname),count(distinct t1.libname) as a
+       from t3 left join t1 on t3.libname=t1.libname left join t2
+       on t3.isbn=t2.isbn group by city having count(distinct
+       t1.libname) > 1;
+#
+# Wrong result, see bug#49872
+# 
+SELECT @bar;
+
 drop table t1, t2, t3;
 
 #

mysql-test/t/user_var.test

@@ -248,4 +248,24 @@ SELECT @a, @b;
 SELECT a, b FROM t1 WHERE a=2 AND b=3 GROUP BY a, b;
 DROP TABLE t1;
 
+#
+# Bug#47371: reference by same column name
+#
+CREATE TABLE t1 (f1 int(11) default NULL, f2 int(11) default NULL);
+CREATE TABLE t2 (f1 int(11) default NULL, f2 int(11) default NULL, foo int(11));
+CREATE TABLE t3 (f1 int(11) default NULL, f2 int(11) default NULL);
+
+INSERT INTO t1 VALUES(10, 10);
+INSERT INTO t1 VALUES(10, 10);
+INSERT INTO t2 VALUES(10, 10, 10);
+INSERT INTO t2 VALUES(10, 10, 10);
+INSERT INTO t3 VALUES(10, 10);
+INSERT INTO t3 VALUES(10, 10);
+
+SELECT MIN(t2.f1),
+@bar:= (SELECT MIN(t3.f2) FROM t3 WHERE t3.f2 > foo)
+FROM t1,t2 WHERE t1.f1 = t2.f1 ORDER BY t2.f1;
+
+DROP TABLE t1, t2, t3;
+
 --echo End of 5.0 tests

sql/item_func.cc

@@ -610,7 +610,7 @@ void Item_func::signal_divide_by_null()
 
 Item *Item_func::get_tmp_table_item(THD *thd)
 {
-  if (!with_sum_func && !const_item() && functype() != SUSERVAR_FUNC)
+  if (!with_sum_func && !const_item())
     return new Item_field(result_field);
   return copy_or_same(thd);
 }