MDEV-36592: In JOIN ... USING(columns), query plan depends on join order

"t1 JOIN t2 USING(col1,...)" calls mark_common_columns() to mark the
listed columns as used in both used tables, t1 and t2.

Due to a typo bug, it would mark the wrong column in the second table
(t2): instead of t2.col1 it would mark the last column in t2.

The harmful effects included JOIN_TAB(t2)->covering_keys not being
set correctly. This changed the cost to access the table and then
caused different query plans depending on which table was the second
in the JOIN ... USING syntax.

Author: spetrunia

mysql-test/main/join.result

@@ -3611,3 +3611,32 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	100	Using where
 1	SIMPLE	t2	ref	kp1	kp1	5	test.t1.a	1	Using index condition
 drop table t1,t2;
+#
+# MDEV-36592: If the join_condition is specified via USING (column_list), the query plan depends ...
+#
+CREATE TABLE t1 (
+id int(11),
+f1 char(255),
+PRIMARY KEY  (id)
+);
+INSERT INTO t1 (id) VALUES (1),(2),(3);
+UPDATE t1 SET f1=REPEAT('a',250);
+CREATE TABLE t2 (id  int(11), f2 INT NOT NULL);
+INSERT INTO t2 select seq, seq from seq_1_to_20;
+ANALYZE TABLE t1, t2;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	Engine-independent statistics collected
+test.t1	analyze	status	OK
+test.t2	analyze	status	Engine-independent statistics collected
+test.t2	analyze	status	OK
+# In both queries, t1 should use type=index, not type=ALL:
+EXPLAIN SELECT count(*) FROM t2 JOIN t1 USING (id);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index	PRIMARY	PRIMARY	4	NULL	3	Using index
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	20	Using where; Using join buffer (flat, BNL join)
+EXPLAIN SELECT count(*) FROM t1 JOIN t2 USING (id);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index	PRIMARY	PRIMARY	4	NULL	3	Using index
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	20	Using where; Using join buffer (flat, BNL join)
+DROP TABLE t1,t2;
+# End of 10.11 tests

mysql-test/main/join.test

@@ -2015,3 +2015,28 @@ where
   t2.kp1=t1.a and t2.kp1<=100 and t2.kp2<=20;
 
 drop table t1,t2;
+
+--echo #
+--echo # MDEV-36592: If the join_condition is specified via USING (column_list), the query plan depends ...
+--echo #
+CREATE TABLE t1 (
+  id int(11),
+  f1 char(255),
+  PRIMARY KEY  (id)
+);
+INSERT INTO t1 (id) VALUES (1),(2),(3);
+UPDATE t1 SET f1=REPEAT('a',250);
+
+CREATE TABLE t2 (id  int(11), f2 INT NOT NULL);
+INSERT INTO t2 select seq, seq from seq_1_to_20;
+
+ANALYZE TABLE t1, t2;
+
+--echo # In both queries, t1 should use type=index, not type=ALL:
+EXPLAIN SELECT count(*) FROM t2 JOIN t1 USING (id);
+EXPLAIN SELECT count(*) FROM t1 JOIN t2 USING (id);
+
+DROP TABLE t1,t2;
+
+--echo # End of 10.11 tests
+

sql/sql_base.cc

@@ -7414,6 +7414,9 @@ mark_common_columns(THD *thd, TABLE_LIST *table_ref_1, TABLE_LIST *table_ref_2,
     if (!found)
       continue;                                 // No matching field
 
+    /* Restore field_2 to point to the field which was a match for field_1. */
+    field_2= nj_col_2->field();
+
     /*
       field_1 and field_2 have the same names. Check if they are in the USING
       clause (if present), mark them as common fields, and add a new