be sure to call top_level_item() on the new Item_cond_and,

that merges ON and WHERE (BUG#10162)

mysql-test/r/join_outer.result

@@ -943,3 +943,17 @@ Warnings:
 Warning	1260	2 line(s) were cut by GROUP_CONCAT()
 drop table t1, t2;
 set group_concat_max_len=default;
+create table t1 (gid smallint(5) unsigned not null, x int(11) not null, y int(11) not null, art int(11) not null, primary key  (gid,x,y));
+insert t1 values (1, -5, -8, 2), (1, 2, 2, 1), (1, 1, 1, 1);
+create table t2 (gid smallint(5) unsigned not null, x int(11) not null, y int(11) not null, id int(11) not null, primary key  (gid,id,x,y), key id (id));
+insert t2 values (1, -5, -8, 1), (1, 1, 1, 1), (1, 2, 2, 1);
+create table t3 ( set_id smallint(5) unsigned not null, id tinyint(4) unsigned not null, name char(12) not null, primary key  (id,set_id));
+insert t3 values (0, 1, 'a'), (1, 1, 'b'), (0, 2, 'c'), (1, 2, 'd'), (1, 3, 'e'), (1, 4, 'f'), (1, 5, 'g'), (1, 6, 'h');
+explain select name from t1 left join t2 on t1.x = t2.x and t1.y = t2.y
+left join t3 on t1.art = t3.id where t2.id =1 and t2.x = -5 and t2.y =-8
+and t1.gid =1 and t2.gid =1 and t3.set_id =1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	const	PRIMARY	PRIMARY	10	const,const,const	1	
+1	SIMPLE	t2	const	PRIMARY,id	PRIMARY	14	const,const,const,const	1	Using index
+1	SIMPLE	t3	const	PRIMARY	PRIMARY	3	const,const	1	
+drop tables t1,t2,t3;

mysql-test/t/join_outer.test

@@ -661,3 +661,18 @@ select group_concat(t1.b,t2.c) from t1 left join t2 using(a) group by t1.a;
 select group_concat(t1.b,t2.c) from t1 inner join t2 using(a) group by t1.a;
 drop table t1, t2;
 set group_concat_max_len=default;
+
+#
+# BUG#10162 - ON is merged with WHERE, left join is convered to a regular join
+#
+create table t1 (gid smallint(5) unsigned not null, x int(11) not null, y int(11) not null, art int(11) not null, primary key  (gid,x,y));
+insert t1 values (1, -5, -8, 2), (1, 2, 2, 1), (1, 1, 1, 1);
+create table t2 (gid smallint(5) unsigned not null, x int(11) not null, y int(11) not null, id int(11) not null, primary key  (gid,id,x,y), key id (id));
+insert t2 values (1, -5, -8, 1), (1, 1, 1, 1), (1, 2, 2, 1);
+create table t3 ( set_id smallint(5) unsigned not null, id tinyint(4) unsigned not null, name char(12) not null, primary key  (id,set_id));
+insert t3 values (0, 1, 'a'), (1, 1, 'b'), (0, 2, 'c'), (1, 2, 'd'), (1, 3, 'e'), (1, 4, 'f'), (1, 5, 'g'), (1, 6, 'h');
+explain select name from t1 left join t2 on t1.x = t2.x and t1.y = t2.y
+left join t3 on t1.art = t3.id where t2.id =1 and t2.x = -5 and t2.y =-8
+and t1.gid =1 and t2.gid =1 and t3.set_id =1;
+drop tables t1,t2,t3;
+

sql/sql_select.cc

@@ -7396,6 +7396,7 @@ simplify_joins(JOIN *join, List<TABLE_LIST> *join_list, COND *conds, bool top)
         if (conds)
         {
           conds= and_conds(conds, table->on_expr);
+          conds->top_level_item();
           /* conds is always a new item as both cond and on_expr existed */
           DBUG_ASSERT(!conds->fixed);
           conds->fix_fields(join->thd, 0, &conds);