MDEV-5056: Wrong result (extra rows) with materialization+semijoin, IN subqueries

Apply fix suggested by Igor:
- When eliminate_item_equal() generates pair-wise equalities from a 
  multi-equality,  do generate a "bridge" equality between the first 
  field inside SJM nest and the field that's first in the overall multi-equality.

mysql-test/r/subselect_mat.result

@@ -2038,6 +2038,27 @@ SELECT * FROM t1 WHERE 8 IN (SELECT MIN(pk) FROM t1) AND (pk = a OR pk = b);
 pk	a	b
 DROP TABLE t1;
 # End of 5.3 tests
+#
+# MDEV-5056: Wrong result (extra rows) with materialization+semijoin, IN subqueries
+#
+set @tmp_mdev5056=@@join_cache_level;
+SET join_cache_level = 2;
+CREATE TABLE t1 ( c1 VARCHAR(2), c2 VARCHAR(2), INDEX(c1) ) ENGINE=MyISAM;
+INSERT INTO t1 VALUES 
+('JP','OM'),('VA','JP'),('CA','ML'),('ML','EG'),('DK','CA'),
+('DK','QA'),('YE','PL'),('TR','ZW'),('DK','SK'),('SK','DK'),
+('RO','ML'),('ML','BG'),('BG','ZW'),('ZW','GE'),('GE','JP'),
+('PL','EG'),('QA','YE'),('WF','DK'),('DK','JP'),('EG','OM');
+CREATE TABLE t2 ( c3 VARCHAR(2), c4 VARCHAR(2) ) ENGINE=MyISAM;
+INSERT INTO t2 VALUES ('CA','ML'),('IN','HU'),('HU','IN');
+SELECT * FROM t1 AS alias1, t1 AS alias2 
+WHERE ( alias2.c2, alias1.c1 ) IN ( SELECT c4, c3 FROM t2 ) AND alias1.c1 IN ( SELECT c2 FROM t1 );
+c1	c2	c1	c2
+CA	ML	CA	ML
+CA	ML	RO	ML
+DROP TABLE t1,t2;
+set join_cache_level=@tmp_mdev5056;
+# End of 5.5 tests
 set @subselect_mat_test_optimizer_switch_value=null;
 set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';
 set optimizer_switch='mrr=on,mrr_sort_keys=on,index_condition_pushdown=on';

mysql-test/r/subselect_sj_mat.result

@@ -2078,3 +2078,24 @@ SELECT * FROM t1 WHERE 8 IN (SELECT MIN(pk) FROM t1) AND (pk = a OR pk = b);
 pk	a	b
 DROP TABLE t1;
 # End of 5.3 tests
+#
+# MDEV-5056: Wrong result (extra rows) with materialization+semijoin, IN subqueries
+#
+set @tmp_mdev5056=@@join_cache_level;
+SET join_cache_level = 2;
+CREATE TABLE t1 ( c1 VARCHAR(2), c2 VARCHAR(2), INDEX(c1) ) ENGINE=MyISAM;
+INSERT INTO t1 VALUES 
+('JP','OM'),('VA','JP'),('CA','ML'),('ML','EG'),('DK','CA'),
+('DK','QA'),('YE','PL'),('TR','ZW'),('DK','SK'),('SK','DK'),
+('RO','ML'),('ML','BG'),('BG','ZW'),('ZW','GE'),('GE','JP'),
+('PL','EG'),('QA','YE'),('WF','DK'),('DK','JP'),('EG','OM');
+CREATE TABLE t2 ( c3 VARCHAR(2), c4 VARCHAR(2) ) ENGINE=MyISAM;
+INSERT INTO t2 VALUES ('CA','ML'),('IN','HU'),('HU','IN');
+SELECT * FROM t1 AS alias1, t1 AS alias2 
+WHERE ( alias2.c2, alias1.c1 ) IN ( SELECT c4, c3 FROM t2 ) AND alias1.c1 IN ( SELECT c2 FROM t1 );
+c1	c2	c1	c2
+CA	ML	CA	ML
+CA	ML	RO	ML
+DROP TABLE t1,t2;
+set join_cache_level=@tmp_mdev5056;
+# End of 5.5 tests

mysql-test/t/subselect_sj_mat.test

@@ -1726,3 +1726,29 @@ SELECT * FROM t1 WHERE 8 IN (SELECT MIN(pk) FROM t1) AND (pk = a OR pk = b);
 DROP TABLE t1;
 
 --echo # End of 5.3 tests
+
+
+--echo #
+--echo # MDEV-5056: Wrong result (extra rows) with materialization+semijoin, IN subqueries
+--echo #
+set @tmp_mdev5056=@@join_cache_level;
+SET join_cache_level = 2;
+
+CREATE TABLE t1 ( c1 VARCHAR(2), c2 VARCHAR(2), INDEX(c1) ) ENGINE=MyISAM;
+INSERT INTO t1 VALUES 
+('JP','OM'),('VA','JP'),('CA','ML'),('ML','EG'),('DK','CA'),
+('DK','QA'),('YE','PL'),('TR','ZW'),('DK','SK'),('SK','DK'),
+('RO','ML'),('ML','BG'),('BG','ZW'),('ZW','GE'),('GE','JP'),
+('PL','EG'),('QA','YE'),('WF','DK'),('DK','JP'),('EG','OM');
+
+CREATE TABLE t2 ( c3 VARCHAR(2), c4 VARCHAR(2) ) ENGINE=MyISAM;
+INSERT INTO t2 VALUES ('CA','ML'),('IN','HU'),('HU','IN');
+
+SELECT * FROM t1 AS alias1, t1 AS alias2 
+WHERE ( alias2.c2, alias1.c1 ) IN ( SELECT c4, c3 FROM t2 ) AND alias1.c1 IN ( SELECT c2 FROM t1 );
+
+DROP TABLE t1,t2;
+set join_cache_level=@tmp_mdev5056;
+
+--echo # End of 5.5 tests
+

sql/sql_select.cc

@@ -12295,12 +12295,14 @@ Item *eliminate_item_equal(COND *cond, COND_EQUAL *upper_levels,
       /*
         If we're inside an SJM-nest (current_sjm!=NULL), and the multi-equality
         doesn't include a constant, we should produce equality with the first
-        of the equals in this SJM.
+        of the equal items in this SJM (except for the first element inside the
+        SJM. For that, we produce the equality with the "head" item).
 
         In other cases, get the "head" item, which is either first of the
         equals on top level, or the constant.
       */
-      Item *head_item= (!item_const && current_sjm)? current_sjm_head: head;
+      Item *head_item= (!item_const && current_sjm && 
+                        current_sjm_head != field_item) ? current_sjm_head: head; 
       Item *head_real_item=  head_item->real_item();
       if (head_real_item->type() == Item::FIELD_ITEM)
         head_item= head_real_item;