MDEV-16726 Assertion `tab->type == JT_REF || tab->type == JT_EQ_REF' failed

Due to a legacy bug in the code of make_join_statistics() detecting
so-called constant tables could miss some of them in rare queries
that used RIGHT JOIN. As a result these queries had execution plans
different from the execution plans of the equivalent queries with
LEFT JOIN.
Besides starting from 10.2 this could trigger an assertion failure.

mysql-test/r/join_outer.result

@@ -2368,5 +2368,55 @@ id	sid	id
 1	NULL	NULL
 2	NULL	NULL
 drop table t1, t2;
+#
+# MDEV-16726: SELECT with STRAGHT JOIN containing NESTED RIGHT JOIN
+#             converted to INNER JOIN with first constant inner table
+#
+CREATE TABLE t1 (
+pk int PRIMARY KEY, i1 int, v1 varchar(1), v2 varchar(1), KEY v1 (v1,i1)
+) engine=MyISAM;
+INSERT INTO t1 VALUES
+(8,3,'c','c'),(9,4,'z','z'),(10,3,'i','i'),(11,186,'x','x'),
+(14,226,'m','m'),(15,133,'p','p');
+CREATE TABLE t2 (
+pk int PRIMARY KEY, i1 int, v1 varchar(1), v2 varchar(1)
+) engine=MyISAM;
+INSERT INTO t2 VALUES (10,6,'p','p');
+EXPLAIN EXTENDED
+SELECT STRAIGHT_JOIN t2.v2
+FROM
+(t1 as tb1 LEFT JOIN t1 AS tb2 ON tb2.v1 = tb1.v2)
+RIGHT JOIN
+(t2,t1)
+ON t1.pk = t2.pk AND t2.v2 = tb1.v1
+WHERE tb1.pk = 40
+ORDER BY tb1.i1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+Warnings:
+Note	1003	select straight_join 'p' AS `v2` from `test`.`t1` join `test`.`t1` `tb1` left join `test`.`t1` `tb2` on(multiple equal(`test`.`tb2`.`v1`, NULL)) where 0 order by NULL
+EXPLAIN EXTENDED
+SELECT STRAIGHT_JOIN t2.v2
+FROM
+(t2,t1)
+LEFT JOIN
+(t1 as tb1 LEFT JOIN t1 AS tb2 ON tb2.v1 = tb1.v2)
+ON t1.pk = t2.pk AND t2.v2 = tb1.v1
+WHERE tb1.pk = 40
+ORDER BY tb1.i1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+Warnings:
+Note	1003	select straight_join 'p' AS `v2` from `test`.`t1` join `test`.`t1` `tb1` left join `test`.`t1` `tb2` on(multiple equal(`test`.`tb2`.`v1`, NULL)) where 0 order by NULL
+SELECT STRAIGHT_JOIN DISTINCT t2.v2
+FROM
+(t1 as tb1 LEFT JOIN t1 AS tb2 ON tb2.v1 = tb1.v2)
+RIGHT JOIN
+(t2,t1)
+ON t1.pk = t2.pk AND t2.v2 = tb1.v1
+WHERE tb1.pk = 40
+ORDER BY tb1.i1;
+v2
+DROP TABLE t1,t2;
 # end of 5.5 tests
 SET optimizer_switch=@save_optimizer_switch;

mysql-test/r/join_outer_jcl6.result

@@ -2379,6 +2379,56 @@ id	sid	id
 1	NULL	NULL
 2	NULL	NULL
 drop table t1, t2;
+#
+# MDEV-16726: SELECT with STRAGHT JOIN containing NESTED RIGHT JOIN
+#             converted to INNER JOIN with first constant inner table
+#
+CREATE TABLE t1 (
+pk int PRIMARY KEY, i1 int, v1 varchar(1), v2 varchar(1), KEY v1 (v1,i1)
+) engine=MyISAM;
+INSERT INTO t1 VALUES
+(8,3,'c','c'),(9,4,'z','z'),(10,3,'i','i'),(11,186,'x','x'),
+(14,226,'m','m'),(15,133,'p','p');
+CREATE TABLE t2 (
+pk int PRIMARY KEY, i1 int, v1 varchar(1), v2 varchar(1)
+) engine=MyISAM;
+INSERT INTO t2 VALUES (10,6,'p','p');
+EXPLAIN EXTENDED
+SELECT STRAIGHT_JOIN t2.v2
+FROM
+(t1 as tb1 LEFT JOIN t1 AS tb2 ON tb2.v1 = tb1.v2)
+RIGHT JOIN
+(t2,t1)
+ON t1.pk = t2.pk AND t2.v2 = tb1.v1
+WHERE tb1.pk = 40
+ORDER BY tb1.i1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+Warnings:
+Note	1003	select straight_join 'p' AS `v2` from `test`.`t1` join `test`.`t1` `tb1` left join `test`.`t1` `tb2` on(multiple equal(`test`.`tb2`.`v1`, NULL)) where 0 order by NULL
+EXPLAIN EXTENDED
+SELECT STRAIGHT_JOIN t2.v2
+FROM
+(t2,t1)
+LEFT JOIN
+(t1 as tb1 LEFT JOIN t1 AS tb2 ON tb2.v1 = tb1.v2)
+ON t1.pk = t2.pk AND t2.v2 = tb1.v1
+WHERE tb1.pk = 40
+ORDER BY tb1.i1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+Warnings:
+Note	1003	select straight_join 'p' AS `v2` from `test`.`t1` join `test`.`t1` `tb1` left join `test`.`t1` `tb2` on(multiple equal(`test`.`tb2`.`v1`, NULL)) where 0 order by NULL
+SELECT STRAIGHT_JOIN DISTINCT t2.v2
+FROM
+(t1 as tb1 LEFT JOIN t1 AS tb2 ON tb2.v1 = tb1.v2)
+RIGHT JOIN
+(t2,t1)
+ON t1.pk = t2.pk AND t2.v2 = tb1.v1
+WHERE tb1.pk = 40
+ORDER BY tb1.i1;
+v2
+DROP TABLE t1,t2;
 # end of 5.5 tests
 SET optimizer_switch=@save_optimizer_switch;
 set join_cache_level=default;

mysql-test/r/subselect_mat_cost_bugs.result

@@ -442,7 +442,7 @@ SELECT i2 FROM t2 RIGHT JOIN t3 ON (c3 = c2) WHERE pk3 = i1
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	system	NULL	NULL	NULL	NULL	1	
 2	DEPENDENT SUBQUERY	t3	const	PRIMARY	PRIMARY	4	const	1	
-2	DEPENDENT SUBQUERY	t2	index	NULL	i2	11	NULL	2	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	index	i2	i2	11	NULL	2	Using where; Using index
 DROP TABLE t1,t2,t3;
 #
 # MDEV-7599: in-to-exists chosen after min/max optimization

mysql-test/t/join_outer.test

@@ -1911,6 +1911,54 @@ select * from t1 t
  on t.id=r.id ;
 drop table t1, t2;
 
+--echo #
+--echo # MDEV-16726: SELECT with STRAGHT JOIN containing NESTED RIGHT JOIN
+--echo #             converted to INNER JOIN with first constant inner table
+--echo #
+
+CREATE TABLE t1 (
+  pk int PRIMARY KEY, i1 int, v1 varchar(1), v2 varchar(1), KEY v1 (v1,i1)
+) engine=MyISAM;
+INSERT INTO t1 VALUES
+  (8,3,'c','c'),(9,4,'z','z'),(10,3,'i','i'),(11,186,'x','x'),
+  (14,226,'m','m'),(15,133,'p','p');
+
+CREATE TABLE t2 (
+  pk int PRIMARY KEY, i1 int, v1 varchar(1), v2 varchar(1)
+) engine=MyISAM;
+INSERT INTO t2 VALUES (10,6,'p','p');
+
+EXPLAIN EXTENDED
+SELECT STRAIGHT_JOIN t2.v2
+FROM
+  (t1 as tb1 LEFT JOIN t1 AS tb2 ON tb2.v1 = tb1.v2)
+  RIGHT JOIN
+  (t2,t1)
+  ON t1.pk = t2.pk AND t2.v2 = tb1.v1
+WHERE tb1.pk = 40
+ORDER BY tb1.i1;
+
+EXPLAIN EXTENDED
+SELECT STRAIGHT_JOIN t2.v2
+FROM
+    (t2,t1)
+    LEFT JOIN
+    (t1 as tb1 LEFT JOIN t1 AS tb2 ON tb2.v1 = tb1.v2)
+   ON t1.pk = t2.pk AND t2.v2 = tb1.v1
+WHERE tb1.pk = 40
+ORDER BY tb1.i1;
+
+SELECT STRAIGHT_JOIN DISTINCT t2.v2
+FROM
+  (t1 as tb1 LEFT JOIN t1 AS tb2 ON tb2.v1 = tb1.v2)
+  RIGHT JOIN
+  (t2,t1)
+  ON t1.pk = t2.pk AND t2.v2 = tb1.v1
+WHERE tb1.pk = 40
+ORDER BY tb1.i1;
+
+DROP TABLE t1,t2;
+
 --echo # end of 5.5 tests
 
 SET optimizer_switch=@save_optimizer_switch;

sql/sql_select.cc

@@ -3456,8 +3456,8 @@ make_join_statistics(JOIN *join, List<TABLE_LIST> &tables_list,
   int ref_changed;
   do
   {
-  more_const_tables_found:
     ref_changed = 0;
+  more_const_tables_found:
     found_ref=0;
 
     /*
@@ -3622,7 +3622,7 @@ make_join_statistics(JOIN *join, List<TABLE_LIST> &tables_list,
 	}
       }
     }
-  } while (join->const_table_map & found_ref && ref_changed);
+  } while (ref_changed);
  
   join->sort_by_table= get_sort_by_table(join->order, join->group_list,
                                          join->select_lex->leaf_tables,