Fixed bug mdev-4220.

This bug is a regression bug. The regression was introduced by
the patch for mdev-3851, that tried to weaken the condition when
a ref access with an extended key can be converted to an eq_ref
access. The patch incorrectly formed this condition. As a result,
while improving performance for some queries, the patch caused 
worse performance for another queries.

mysql-test/r/innodb_ext_key.result

@@ -731,6 +731,7 @@ CREATE TABLE t2 (b int) ENGINE=MyISAM;
 INSERT INTO t1 (a) VALUES (4), (6);
 INSERT INTO t2 (b) VALUES (0), (8);
 set @save_optimizer_switch=@@optimizer_switch;
+set @save_join_cache_level=@@join_cache_level;
 SET join_cache_level=3;
 SET optimizer_switch='join_cache_hashed=on';
 SET optimizer_switch='join_cache_bka=on';
@@ -742,6 +743,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t2	hash_ALL	NULL	#hash#$hj	5	test.t1.a	2	Using where; Using join buffer (flat, BNLH join)
 SELECT * FROM t1, t2 WHERE b=a;
 a	b
+set join_cache_level=@save_join_cache_level;
 set optimizer_switch=@save_optimizer_switch;
 DROP TABLE t1,t2;
 #
@@ -772,5 +774,97 @@ INSERT INTO t1 (c2, c3, c4) VALUES (58291525, 2580, 'foobar')
 ON DUPLICATE KEY UPDATE c4 = VALUES(c4);
 set optimizer_switch=@save_optimizer_switch;
 DROP TABLE t1;
+#
+# Bug mdev-4220: using ref instead of eq_ref
+#                with extended_keys=on   
+# (performance regression introduced in the patch for mdev-3851)
+#
+set @save_optimizer_switch=@@optimizer_switch;
+create table t1 (a int not null) engine=innodb;
+insert into t1 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+create table t2 (
+pk int primary key, a int not null, b int, unique(a)
+)engine=innodb;
+insert into t2
+select 
+A.a + 10 * B.a, A.a + 10 * B.a, A.a + 10 * B.a 
+from t1 A, t1 B;
+set optimizer_switch='extended_keys=off';
+explain 
+select * from t1, t2 where t2.a=t1.a and t2.b < 2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	10	
+1	SIMPLE	t2	eq_ref	a	a	4	test.t1.a	1	Using where
+flush status;
+select * from t1, t2 where t2.a=t1.a and t2.b < 2;
+a	pk	a	b
+0	0	0	0
+1	1	1	1
+show status like 'handler_read%';
+Variable_name	Value
+Handler_read_first	0
+Handler_read_key	10
+Handler_read_last	0
+Handler_read_next	0
+Handler_read_prev	0
+Handler_read_rnd	0
+Handler_read_rnd_deleted	0
+Handler_read_rnd_next	11
+set optimizer_switch='extended_keys=on';
+explain 
+select * from t1, t2 where t2.a=t1.a and t2.b < 2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	10	
+1	SIMPLE	t2	eq_ref	a	a	4	test.t1.a	1	Using where
+flush status;
+select * from t1, t2 where t2.a=t1.a and t2.b < 2;
+a	pk	a	b
+0	0	0	0
+1	1	1	1
+show status like 'handler_read%';
+Variable_name	Value
+Handler_read_first	0
+Handler_read_key	10
+Handler_read_last	0
+Handler_read_next	0
+Handler_read_prev	0
+Handler_read_rnd	0
+Handler_read_rnd_deleted	0
+Handler_read_rnd_next	11
+drop table t1,t2;
+create table t1(a int) engine=myisam;
+insert into t1 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+create table t2(a int) engine=myisam;
+insert into t2 select A.a + 10*B.a + 100*C.a from t1 A, t1 B, t1 C;
+create table t3 (
+pk1 int not null, pk2 int not null, col1 int not null, col2 int not null)
+engine=innodb;
+insert into t3 select a,a,a,a from t2;
+alter table t3 add primary key (pk1, pk2);
+alter table t3 add  key (col1, col2);
+set optimizer_switch='extended_keys=off';
+explain 
+select * from t1, t3 where t3.col1=t1.a and  t3.col2=t1.a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	#	Using where
+1	SIMPLE	t3	ref	col1	col1	8	test.t1.a,test.t1.a	#	Using index
+explain 
+select * from t1, t3 where t3.col1=t1.a and  t3.col2=t1.a and t3.pk1=t1.a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	#	Using where
+1	SIMPLE	t3	ref	PRIMARY,col1	PRIMARY	4	test.t1.a	#	Using where
+set optimizer_switch='extended_keys=on';
+explain 
+select * from t1, t3 where t3.col1=t1.a and  t3.col2=t1.a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	#	Using where
+1	SIMPLE	t3	ref	col1	col1	8	test.t1.a,test.t1.a	#	Using index
+explain 
+select * from t1, t3 where t3.col1=t1.a and  t3.col2=t1.a and t3.pk1=t1.a;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	#	Using where
+1	SIMPLE	t3	ref	PRIMARY,col1	col1	12	test.t1.a,test.t1.a,test.t1.a	#	Using index
+drop table t1,t2,t3;
+set optimizer_switch=@save_optimizer_switch;
 set optimizer_switch=@save_ext_key_optimizer_switch;
 SET SESSION STORAGE_ENGINE=DEFAULT;

mysql-test/t/innodb_ext_key.test

@@ -414,6 +414,7 @@ INSERT INTO t1 (a) VALUES (4), (6);
 INSERT INTO t2 (b) VALUES (0), (8);
 
 set @save_optimizer_switch=@@optimizer_switch;
+set @save_join_cache_level=@@join_cache_level;
 
 SET join_cache_level=3;
 SET optimizer_switch='join_cache_hashed=on';
@@ -424,6 +425,7 @@ EXPLAIN
 SELECT * FROM t1, t2 WHERE b=a;
 SELECT * FROM t1, t2 WHERE b=a;
 
+set join_cache_level=@save_join_cache_level;
 set optimizer_switch=@save_optimizer_switch;
 
 DROP TABLE t1,t2;
@@ -466,6 +468,78 @@ set optimizer_switch=@save_optimizer_switch;
 
 DROP TABLE t1;
 
+--echo #
+--echo # Bug mdev-4220: using ref instead of eq_ref
+--echo #                with extended_keys=on   
+--echo # (performance regression introduced in the patch for mdev-3851)
+--echo #
+
+set @save_optimizer_switch=@@optimizer_switch;
+
+create table t1 (a int not null) engine=innodb;
+
+insert into t1 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+
+create table t2 (
+  pk int primary key, a int not null, b int, unique(a)
+)engine=innodb;
+
+insert into t2
+select 
+  A.a + 10 * B.a, A.a + 10 * B.a, A.a + 10 * B.a 
+from t1 A, t1 B;
+
+set optimizer_switch='extended_keys=off';
+explain 
+select * from t1, t2 where t2.a=t1.a and t2.b < 2;
+flush status;
+select * from t1, t2 where t2.a=t1.a and t2.b < 2;
+show status like 'handler_read%';
+
+set optimizer_switch='extended_keys=on';
+explain 
+select * from t1, t2 where t2.a=t1.a and t2.b < 2;
+flush status;
+select * from t1, t2 where t2.a=t1.a and t2.b < 2;
+show status like 'handler_read%';
+
+drop table t1,t2;
+
+# this test case did not demonstrate any regression
+# it is added for better testing
+
+create table t1(a int) engine=myisam;
+insert into t1 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+
+create table t2(a int) engine=myisam;
+insert into t2 select A.a + 10*B.a + 100*C.a from t1 A, t1 B, t1 C;
+
+create table t3 (
+  pk1 int not null, pk2 int not null, col1 int not null, col2 int not null)
+engine=innodb;
+insert into t3 select a,a,a,a from t2;
+alter table t3 add primary key (pk1, pk2);
+alter table t3 add  key (col1, col2);
+
+set optimizer_switch='extended_keys=off';
+--replace_column 9 #
+explain 
+select * from t1, t3 where t3.col1=t1.a and  t3.col2=t1.a;
+--replace_column 9 #
+explain 
+select * from t1, t3 where t3.col1=t1.a and  t3.col2=t1.a and t3.pk1=t1.a;
+
+set optimizer_switch='extended_keys=on';
+--replace_column 9 #
+explain 
+select * from t1, t3 where t3.col1=t1.a and  t3.col2=t1.a;
+--replace_column 9 #
+explain 
+select * from t1, t3 where t3.col1=t1.a and  t3.col2=t1.a and t3.pk1=t1.a;
+
+drop table t1,t2,t3;
+
+set optimizer_switch=@save_optimizer_switch;
+
 set optimizer_switch=@save_ext_key_optimizer_switch;
 SET SESSION STORAGE_ENGINE=DEFAULT;
-

sql/sql_select.cc

@@ -7987,20 +7987,17 @@ static bool create_ref_for_key(JOIN *join, JOIN_TAB *j,
   ulong key_flags= j->table->actual_key_flags(keyinfo);
   if (j->type == JT_CONST)
     j->table->const_table= 1;
-  else if (((key_flags & (HA_NOSAME | HA_NULL_PART_KEY))!= HA_NOSAME) ||
-	   keyparts != j->table->actual_n_key_parts(keyinfo) ||
-           null_ref_key)
-  {
-    if (test(key_flags & HA_EXT_NOSAME) && keyparts == keyinfo->ext_key_parts &&
-        !null_ref_key)
-      j->type= JT_EQ_REF;
-    else
-    {
-      /* Must read with repeat */
-      j->type= null_ref_key ? JT_REF_OR_NULL : JT_REF;
-      j->ref.null_ref_key= null_ref_key;
-      j->ref.null_ref_part= null_ref_part;
-    }
+  else if (!((keyparts == keyinfo->key_parts && 
+              ((key_flags & (HA_NOSAME | HA_NULL_PART_KEY)) == HA_NOSAME)) ||
+	     (keyparts > keyinfo->key_parts &&   // true only for extended keys 
+              test(key_flags & HA_EXT_NOSAME) &&
+              keyparts == keyinfo->ext_key_parts)) ||
+	    null_ref_key)
+  {
+    /* Must read with repeat */
+    j->type= null_ref_key ? JT_REF_OR_NULL : JT_REF;
+    j->ref.null_ref_key= null_ref_key;
+    j->ref.null_ref_part= null_ref_part;
   }
   else if (keyuse_uses_no_tables)
   {

sql/table.cc

@@ -1003,7 +1003,7 @@ static int open_binary_frm(THD *thd, TABLE_SHARE *share, uchar *head,
         }
       }
       if (j == first_key_parts)
-        keyinfo->ext_key_flags= keyinfo->flags | HA_NOSAME | HA_EXT_NOSAME;
+        keyinfo->ext_key_flags= keyinfo->flags | HA_EXT_NOSAME;
     }
     share->ext_key_parts+= keyinfo->ext_key_parts;  
   }