MWL#110: Make EXPLAIN always show materialization separately

- Add Item_in_subselect::get_identifier() that returns subquery's id
- Change select_describe() to produce output in new format
- Update test results (checked)

mysql-test/r/subselect3.result

@@ -1017,10 +1017,11 @@ update t22 set c = '2005-12-08 15:58:27' where a = 255;
 explain select t21.* from t21,t22 where t21.a = t22.a and 
 t22.a in (select t12.a from t11, t12 where t11.a in(255,256) and t11.a = t12.a and t11.c is null) and t22.c is null order by t21.a;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t11	ALL	NULL	NULL	NULL	NULL	8	Using where; Using temporary; Using filesort; Start materialize; Scan
-1	PRIMARY	t12	ALL	NULL	NULL	NULL	NULL	8	Using where; End materialize; Using join buffer
+1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	8	Using temporary; Using filesort
 1	PRIMARY	t21	ALL	NULL	NULL	NULL	NULL	26	Using where; Using join buffer
 1	PRIMARY	t22	ALL	NULL	NULL	NULL	NULL	26	Using where; Using join buffer
+2	SUBQUERY	t11	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t12	ALL	NULL	NULL	NULL	NULL	8	Using where; Using join buffer
 select t21.* from t21,t22 where t21.a = t22.a and 
 t22.a in (select t12.a from t11, t12 where t11.a in(255,256) and t11.a = t12.a and t11.c is null) and t22.c is null order by t21.a;
 a	b	c
@@ -1034,7 +1035,8 @@ select (select max(Y.a) from t1 Y where a in (select a from t1 Z) and a < X.a) a
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	X	ALL	NULL	NULL	NULL	NULL	2	
 2	DEPENDENT SUBQUERY	Y	ALL	NULL	NULL	NULL	NULL	2	Using where
-2	DEPENDENT SUBQUERY	Z	ALL	NULL	NULL	NULL	NULL	2	Materialize
+2	DEPENDENT SUBQUERY	subselect3	eq_ref	unique_key	unique_key	5	func	1	
+3	SUBQUERY	Z	ALL	NULL	NULL	NULL	NULL	2	
 select (select max(Y.a) from t1 Y where a in (select a from t1 Z) and a < X.a) as subq from t1 X;
 subq
 NULL
@@ -1156,8 +1158,9 @@ create table t3 ( a int , filler char(100), key(a));
 insert into t3 select A.a + 10*B.a, 'filler' from t0 A, t0 B;
 explain select * from t3 where a in (select a from t2) and (a > 5 or a < 10);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	2	Using where; Materialize; Scan
+1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	2	
 1	PRIMARY	t3	ref	a	a	5	test.t2.a	1	
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	2	Using where
 select * from t3 where a in (select a from t2);
 a	filler
 1	filler
@@ -1204,8 +1207,9 @@ insert into t3 select A.a + 10*B.a, A.a + 10*B.a, 'filler' from t1 A, t1 B, t1 C
 explain select * from t1, t3 where t3.a in (select a from t2) and (t3.a < 10 or t3.a >30) and t1.a =3;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	10	Using where
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	10	Using where; Materialize; Scan
+1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	10	
 1	PRIMARY	t3	ref	a	a	5	test.t2.a	10	
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	10	Using where
 explain select straight_join * from t1 A, t1 B where A.a in (select a from t2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	A	ALL	NULL	NULL	NULL	NULL	10	Using where
@@ -1233,14 +1237,16 @@ insert into t0 values(1,1);
 explain select * from t0, t3 where t3.a in (select a from t2) and (t3.a < 10 or t3.a >30);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t0	system	NULL	NULL	NULL	NULL	1	
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	10	Using where; Materialize; Scan
+1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	10	
 1	PRIMARY	t3	ref	a	a	5	test.t2.a	10	
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	10	Using where
 create table t4 as select a as x, a as y from t1;
 explain select * from t0, t3 where (t3.a, t3.b) in (select x,y from t4) and (t3.a < 10 or t3.a >30);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t0	system	NULL	NULL	NULL	NULL	1	
-1	PRIMARY	t4	ALL	NULL	NULL	NULL	NULL	10	Using where; Materialize; Scan
+1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	10	
 1	PRIMARY	t3	ref	a	a	5	test.t4.x	10	Using where
+2	SUBQUERY	t4	ALL	NULL	NULL	NULL	NULL	10	Using where
 drop table t0,t1,t2,t3,t4;
 create table t0 (a int);
 insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
@@ -1264,13 +1270,15 @@ set @@optimizer_switch='firstmatch=off';
 explain select * from t1 where (a,b) in (select a,b from t2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	10	
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	100	Materialize
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	10	func	1	
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	100	
 set @save_optimizer_search_depth=@@optimizer_search_depth;
 set @@optimizer_search_depth=63;
 explain select * from t1 where (a,b) in (select a,b from t2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	10	
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	100	Materialize
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	10	func	1	
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	100	
 set @@optimizer_search_depth=@save_optimizer_search_depth;
 set @@optimizer_switch=default;
 drop table t0, t1, t2;
@@ -1308,9 +1316,10 @@ insert into t2 select * from t2;
 explain select * from t1 where (a,b,c) in (select X.a, Y.a, Z.a from t2 X, t2 Y, t2 Z where X.b=33);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	
-1	PRIMARY	X	ALL	NULL	NULL	NULL	NULL	6	Using where; Start materialize
-1	PRIMARY	Y	ALL	NULL	NULL	NULL	NULL	6	Using join buffer
-1	PRIMARY	Z	ALL	NULL	NULL	NULL	NULL	6	End materialize; Using join buffer
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	15	func	1	
+2	SUBQUERY	X	ALL	NULL	NULL	NULL	NULL	6	Using where
+2	SUBQUERY	Y	ALL	NULL	NULL	NULL	NULL	6	Using join buffer
+2	SUBQUERY	Z	ALL	NULL	NULL	NULL	NULL	6	Using join buffer
 drop table t0,t1,t2;
 
 BUG#37842: Assertion in DsMrr_impl::dsmrr_init, at handler.cc:4307
@@ -1380,9 +1389,10 @@ INNER JOIN t2 c ON c.idContact=cona.idContact
 WHERE cona.postalStripped='T2H3B2'
 	);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	cona	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where; Start materialize; Scan
-1	PRIMARY	c	eq_ref	PRIMARY	PRIMARY	4	test.cona.idContact	1	100.00	End materialize
+1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	2	1.00	
 1	PRIMARY	a	index	PRIMARY	PRIMARY	4	NULL	2	100.00	Using where; Using index; Using join buffer
+2	SUBQUERY	cona	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+2	SUBQUERY	c	eq_ref	PRIMARY	PRIMARY	4	test.cona.idContact	1	100.00	
 Warnings:
 Note	1003	select `test`.`a`.`idIndividual` AS `idIndividual` from `test`.`t1` `a` semi join (`test`.`t3` `cona` join `test`.`t2` `c`) where ((`test`.`c`.`idContact` = `test`.`cona`.`idContact`) and (`test`.`a`.`idIndividual` = `test`.`c`.`idObj`) and (`test`.`cona`.`postalStripped` = 'T2H3B2'))
 drop table t1,t2,t3;

mysql-test/r/subselect3_jcl6.result

@@ -1021,10 +1021,11 @@ update t22 set c = '2005-12-08 15:58:27' where a = 255;
 explain select t21.* from t21,t22 where t21.a = t22.a and 
 t22.a in (select t12.a from t11, t12 where t11.a in(255,256) and t11.a = t12.a and t11.c is null) and t22.c is null order by t21.a;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t11	ALL	NULL	NULL	NULL	NULL	8	Using where; Using temporary; Using filesort; Start materialize; Scan
-1	PRIMARY	t12	ALL	NULL	NULL	NULL	NULL	8	Using where; End materialize; Using join buffer
+1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	8	Using temporary; Using filesort
 1	PRIMARY	t21	ALL	NULL	NULL	NULL	NULL	26	Using where; Using join buffer
 1	PRIMARY	t22	ALL	NULL	NULL	NULL	NULL	26	Using where; Using join buffer
+2	SUBQUERY	t11	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t12	ALL	NULL	NULL	NULL	NULL	8	Using where; Using join buffer
 select t21.* from t21,t22 where t21.a = t22.a and 
 t22.a in (select t12.a from t11, t12 where t11.a in(255,256) and t11.a = t12.a and t11.c is null) and t22.c is null order by t21.a;
 a	b	c
@@ -1039,7 +1040,8 @@ select (select max(Y.a) from t1 Y where a in (select a from t1 Z) and a < X.a) a
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	X	ALL	NULL	NULL	NULL	NULL	2	
 2	DEPENDENT SUBQUERY	Y	ALL	NULL	NULL	NULL	NULL	2	Using where
-2	DEPENDENT SUBQUERY	Z	ALL	NULL	NULL	NULL	NULL	2	Materialize
+2	DEPENDENT SUBQUERY	subselect3	eq_ref	unique_key	unique_key	5	func	1	
+3	SUBQUERY	Z	ALL	NULL	NULL	NULL	NULL	2	
 select (select max(Y.a) from t1 Y where a in (select a from t1 Z) and a < X.a) as subq from t1 X;
 subq
 NULL
@@ -1161,8 +1163,9 @@ create table t3 ( a int , filler char(100), key(a));
 insert into t3 select A.a + 10*B.a, 'filler' from t0 A, t0 B;
 explain select * from t3 where a in (select a from t2) and (a > 5 or a < 10);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	2	Using where; Materialize; Scan
+1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	2	
 1	PRIMARY	t3	ref	a	a	5	test.t2.a	1	Using join buffer
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	2	Using where
 select * from t3 where a in (select a from t2);
 a	filler
 1	filler
@@ -1209,8 +1212,9 @@ insert into t3 select A.a + 10*B.a, A.a + 10*B.a, 'filler' from t1 A, t1 B, t1 C
 explain select * from t1, t3 where t3.a in (select a from t2) and (t3.a < 10 or t3.a >30) and t1.a =3;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	10	Using where
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	10	Using where; Materialize; Scan
+1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	10	
 1	PRIMARY	t3	ref	a	a	5	test.t2.a	10	Using join buffer
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	10	Using where
 explain select straight_join * from t1 A, t1 B where A.a in (select a from t2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	A	ALL	NULL	NULL	NULL	NULL	10	Using where
@@ -1238,14 +1242,16 @@ insert into t0 values(1,1);
 explain select * from t0, t3 where t3.a in (select a from t2) and (t3.a < 10 or t3.a >30);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t0	system	NULL	NULL	NULL	NULL	1	
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	10	Using where; Materialize; Scan
+1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	10	
 1	PRIMARY	t3	ref	a	a	5	test.t2.a	10	Using join buffer
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	10	Using where
 create table t4 as select a as x, a as y from t1;
 explain select * from t0, t3 where (t3.a, t3.b) in (select x,y from t4) and (t3.a < 10 or t3.a >30);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t0	system	NULL	NULL	NULL	NULL	1	
-1	PRIMARY	t4	ALL	NULL	NULL	NULL	NULL	10	Using where; Materialize; Scan
+1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	10	
 1	PRIMARY	t3	ref	a	a	5	test.t4.x	10	Using where; Using join buffer
+2	SUBQUERY	t4	ALL	NULL	NULL	NULL	NULL	10	Using where
 drop table t0,t1,t2,t3,t4;
 create table t0 (a int);
 insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
@@ -1269,13 +1275,15 @@ set @@optimizer_switch='firstmatch=off';
 explain select * from t1 where (a,b) in (select a,b from t2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	10	
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	100	Materialize
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	10	func	1	
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	100	
 set @save_optimizer_search_depth=@@optimizer_search_depth;
 set @@optimizer_search_depth=63;
 explain select * from t1 where (a,b) in (select a,b from t2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	10	
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	100	Materialize
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	10	func	1	
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	100	
 set @@optimizer_search_depth=@save_optimizer_search_depth;
 set @@optimizer_switch=default;
 drop table t0, t1, t2;
@@ -1313,9 +1321,10 @@ insert into t2 select * from t2;
 explain select * from t1 where (a,b,c) in (select X.a, Y.a, Z.a from t2 X, t2 Y, t2 Z where X.b=33);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	
-1	PRIMARY	X	ALL	NULL	NULL	NULL	NULL	6	Using where; Start materialize
-1	PRIMARY	Y	ALL	NULL	NULL	NULL	NULL	6	Using join buffer
-1	PRIMARY	Z	ALL	NULL	NULL	NULL	NULL	6	End materialize; Using join buffer
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	15	func	1	
+2	SUBQUERY	X	ALL	NULL	NULL	NULL	NULL	6	Using where
+2	SUBQUERY	Y	ALL	NULL	NULL	NULL	NULL	6	Using join buffer
+2	SUBQUERY	Z	ALL	NULL	NULL	NULL	NULL	6	Using join buffer
 drop table t0,t1,t2;
 
 BUG#37842: Assertion in DsMrr_impl::dsmrr_init, at handler.cc:4307
@@ -1385,9 +1394,10 @@ INNER JOIN t2 c ON c.idContact=cona.idContact
 WHERE cona.postalStripped='T2H3B2'
 	);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	PRIMARY	cona	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where; Start materialize; Scan
-1	PRIMARY	c	eq_ref	PRIMARY	PRIMARY	4	test.cona.idContact	1	100.00	End materialize; Using join buffer
+1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	2	1.00	
 1	PRIMARY	a	index	PRIMARY	PRIMARY	4	NULL	2	100.00	Using where; Using index; Using join buffer
+2	SUBQUERY	cona	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+2	SUBQUERY	c	eq_ref	PRIMARY	PRIMARY	4	test.cona.idContact	1	100.00	Using join buffer
 Warnings:
 Note	1003	select `test`.`a`.`idIndividual` AS `idIndividual` from `test`.`t1` `a` semi join (`test`.`t3` `cona` join `test`.`t2` `c`) where ((`test`.`c`.`idContact` = `test`.`cona`.`idContact`) and (`test`.`a`.`idIndividual` = `test`.`c`.`idObj`) and (`test`.`cona`.`postalStripped` = 'T2H3B2'))
 drop table t1,t2,t3;

mysql-test/r/subselect4.result

@@ -216,8 +216,9 @@ FROM t2
 WHERE PTYPE = 'Design'));
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	t1_IDX	NULL	NULL	NULL	5	
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	6	Using where; Start materialize
-1	PRIMARY	t3	ALL	NULL	NULL	NULL	NULL	12	Using where; End materialize; Using join buffer
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	3	func	1	
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	6	Using where
+2	SUBQUERY	t3	ALL	NULL	NULL	NULL	NULL	12	Using where; Using join buffer
 PREPARE stmt FROM "EXPLAIN SELECT EMPNAME
 FROM t1
 WHERE EMPNUM IN
@@ -230,13 +231,15 @@ WHERE EMPNUM IN
 EXECUTE stmt;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	t1_IDX	NULL	NULL	NULL	5	
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	6	Using where; Start materialize
-1	PRIMARY	t3	ALL	NULL	NULL	NULL	NULL	12	Using where; End materialize; Using join buffer
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	3	func	1	
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	6	Using where
+2	SUBQUERY	t3	ALL	NULL	NULL	NULL	NULL	12	Using where; Using join buffer
 EXECUTE stmt;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ALL	t1_IDX	NULL	NULL	NULL	5	
-1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	6	Using where; Start materialize
-1	SIMPLE	t3	ALL	NULL	NULL	NULL	NULL	12	Using where; End materialize; Using join buffer
+1	SIMPLE	subselect2	eq_ref	unique_key	unique_key	3	func	1	
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	6	Using where
+2	SUBQUERY	t3	ALL	NULL	NULL	NULL	NULL	12	Using where; Using join buffer
 DEALLOCATE PREPARE stmt;
 DROP INDEX t1_IDX ON t1;
 CREATE INDEX t1_IDX ON t1(EMPNUM);
@@ -251,8 +254,9 @@ FROM t2
 WHERE PTYPE = 'Design'));
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	t1_IDX	NULL	NULL	NULL	5	
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	6	Using where; Start materialize
-1	PRIMARY	t3	ALL	NULL	NULL	NULL	NULL	12	Using where; End materialize; Using join buffer
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	3	func	1	
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	6	Using where
+2	SUBQUERY	t3	ALL	NULL	NULL	NULL	NULL	12	Using where; Using join buffer
 PREPARE stmt FROM "EXPLAIN SELECT EMPNAME
 FROM t1
 WHERE EMPNUM IN
@@ -265,13 +269,15 @@ WHERE EMPNUM IN
 EXECUTE stmt;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	t1_IDX	NULL	NULL	NULL	5	
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	6	Using where; Start materialize
-1	PRIMARY	t3	ALL	NULL	NULL	NULL	NULL	12	Using where; End materialize; Using join buffer
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	3	func	1	
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	6	Using where
+2	SUBQUERY	t3	ALL	NULL	NULL	NULL	NULL	12	Using where; Using join buffer
 EXECUTE stmt;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ALL	t1_IDX	NULL	NULL	NULL	5	
-1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	6	Using where; Start materialize
-1	SIMPLE	t3	ALL	NULL	NULL	NULL	NULL	12	Using where; End materialize; Using join buffer
+1	SIMPLE	subselect2	eq_ref	unique_key	unique_key	3	func	1	
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	6	Using where
+2	SUBQUERY	t3	ALL	NULL	NULL	NULL	NULL	12	Using where; Using join buffer
 DEALLOCATE PREPARE stmt;
 DROP INDEX t1_IDX ON t1;
 EXPLAIN SELECT EMPNAME
@@ -285,8 +291,9 @@ FROM t2
 WHERE PTYPE = 'Design'));
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	5	
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	6	Using where; Start materialize
-1	PRIMARY	t3	ALL	NULL	NULL	NULL	NULL	12	Using where; End materialize; Using join buffer
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	3	func	1	
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	6	Using where
+2	SUBQUERY	t3	ALL	NULL	NULL	NULL	NULL	12	Using where; Using join buffer
 PREPARE stmt FROM "EXPLAIN SELECT EMPNAME
 FROM t1
 WHERE EMPNUM IN
@@ -299,13 +306,15 @@ WHERE EMPNUM IN
 EXECUTE stmt;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	5	
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	6	Using where; Start materialize
-1	PRIMARY	t3	ALL	NULL	NULL	NULL	NULL	12	Using where; End materialize; Using join buffer
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	3	func	1	
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	6	Using where
+2	SUBQUERY	t3	ALL	NULL	NULL	NULL	NULL	12	Using where; Using join buffer
 EXECUTE stmt;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	5	
-1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	6	Using where; Start materialize
-1	SIMPLE	t3	ALL	NULL	NULL	NULL	NULL	12	Using where; End materialize; Using join buffer
+1	SIMPLE	subselect2	eq_ref	unique_key	unique_key	3	func	1	
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	6	Using where
+2	SUBQUERY	t3	ALL	NULL	NULL	NULL	NULL	12	Using where; Using join buffer
 DEALLOCATE PREPARE stmt;
 SET SESSION optimizer_switch = @old_optimizer_switch;
 SET SESSION join_cache_level = @old_join_cache_level;

mysql-test/r/subselect_mat.result

@@ -1190,8 +1190,9 @@ INSERT INTO t2 VALUES (13, 1.454);
 SET @@optimizer_switch='default,semijoin=on,materialization=on';
 EXPLAIN SELECT COUNT(*) FROM t1 WHERE (f1,f2) IN (SELECT f1,f2 FROM t2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	2	Materialize; Scan
+1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	2	
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where; Using join buffer
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	2	
 SELECT COUNT(*) FROM t1 WHERE (f1,f2) IN (SELECT f1,f2 FROM t2);
 COUNT(*)
 2
@@ -1211,7 +1212,8 @@ SET @@optimizer_switch='default,semijoin=on,materialization=on';
 EXPLAIN SELECT pk FROM t1 WHERE (a) IN (SELECT a FROM t2 WHERE pk > 0);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	2	
-1	PRIMARY	t2	range	PRIMARY	PRIMARY	4	NULL	2	Using index condition; Using MRR; Materialize
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	5	func	1	
+2	SUBQUERY	t2	range	PRIMARY	PRIMARY	4	NULL	2	Using index condition; Using MRR
 SELECT pk FROM t1 WHERE (a) IN (SELECT a FROM t2 WHERE pk > 0);
 pk
 2

mysql-test/r/subselect_sj.result

@@ -848,7 +848,8 @@ INSERT INTO t2 VALUES (1,'i','iiii','iiii','iiii','iiii','ffff','ffff','ffff','f
 EXPLAIN EXTENDED SELECT pk FROM t1 WHERE (a, b) IN (SELECT a, b FROM t2 WHERE pk > 0);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	
-1	PRIMARY	t2	range	PRIMARY	PRIMARY	4	NULL	2	100.00	Using index condition; Using MRR; Materialize
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	13	func	1	1.00	
+2	SUBQUERY	t2	range	PRIMARY	PRIMARY	4	NULL	2	100.00	Using index condition; Using MRR
 Warnings:
 Note	1003	select `test`.`t1`.`pk` AS `pk` from `test`.`t1` semi join (`test`.`t2`) where ((`test`.`t2`.`pk` > 0))
 SELECT pk FROM t1 WHERE (a, b) IN (SELECT a, b FROM t2 WHERE pk > 0);
@@ -1016,7 +1017,8 @@ FROM t1
 WHERE `varchar_nokey`  < 'n' XOR `pk`  )   ;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	18	100.00	
-1	PRIMARY	t1	ALL	varchar_key	NULL	NULL	NULL	15	100.00	Using where; Materialize
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	8	func	1	1.00	
+2	SUBQUERY	t1	ALL	varchar_key	NULL	NULL	NULL	15	100.00	Using where
 Warnings:
 Note	1003	select `test`.`t2`.`varchar_nokey` AS `varchar_nokey` from `test`.`t2` semi join (`test`.`t1`) where ((`test`.`t1`.`varchar_nokey` = `test`.`t1`.`varchar_key`) and ((`test`.`t1`.`varchar_nokey` < 'n') xor `test`.`t1`.`pk`))
 SELECT varchar_nokey

mysql-test/r/subselect_sj2.result

@@ -32,8 +32,9 @@ a	b
 9	5
 explain select * from t2 where b in (select a from t1);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Materialize; Scan
+1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	3	
 1	PRIMARY	t2	ref	b	b	5	test.t1.a	2	
+2	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	3	
 select * from t2 where b in (select a from t1);
 a	b
 1	1
@@ -73,8 +74,9 @@ A.a + 10*B.a, A.a + 10*B.a, A.a + 10*B.a, A.a + 10*B.a
 from t0 A, t0 B where B.a <5;
 explain select * from t3 where b in (select a from t0);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t0	ALL	NULL	NULL	NULL	NULL	10	Materialize; Scan
+1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	10	
 1	PRIMARY	t3	ref	b	b	5	test.t0.a	1	
+2	SUBQUERY	t0	ALL	NULL	NULL	NULL	NULL	10	
 set @save_ecp= @@engine_condition_pushdown;
 set engine_condition_pushdown=0;
 select * from t3 where b in (select A.a+B.a from t0 A, t0 B where B.a<5);
@@ -99,7 +101,8 @@ set max_heap_table_size= @save_max_heap_table_size;
 explain select * from t1 where a in (select b from t2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	
-1	PRIMARY	t2	index	b	b	5	NULL	10	Using index; Materialize
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	5	func	1	
+2	SUBQUERY	t2	index	b	b	5	NULL	10	Using index
 select * from t1;
 a	b
 1	1
@@ -126,8 +129,9 @@ explain select
 a, mid(filler1, 1,10), length(filler1)=length(filler2) as Z 
 from t1 ot where a in (select a from t2 it);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	it	ALL	NULL	NULL	NULL	NULL	22	Materialize; Scan
+1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	22	
 1	PRIMARY	ot	ALL	NULL	NULL	NULL	NULL	32	Using where; Using join buffer
+2	SUBQUERY	it	ALL	NULL	NULL	NULL	NULL	22	
 select 
 a, mid(filler1, 1,10), length(filler1)=length(filler2) as Z 
 from t1 ot where a in (select a from t2 it);
@@ -159,7 +163,8 @@ a, mid(filler1, 1,10), length(filler1)=length(filler2)
 from t2 ot where a in (select a from t1 it);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	ot	ALL	NULL	NULL	NULL	NULL	22	
-1	PRIMARY	it	ALL	NULL	NULL	NULL	NULL	32	Materialize
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	5	func	1	
+2	SUBQUERY	it	ALL	NULL	NULL	NULL	NULL	32	
 select 
 a, mid(filler1, 1,10), length(filler1)=length(filler2) 
 from t2 ot where a in (select a from t1 it);
@@ -192,8 +197,9 @@ explain select
 a, mid(filler1, 1,10), length(filler1)=length(filler2) as Z 
 from t1 ot where a in (select a from t2 it);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	it	ALL	NULL	NULL	NULL	NULL	22	Materialize; Scan
+1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	22	
 1	PRIMARY	ot	ALL	NULL	NULL	NULL	NULL	52	Using where; Using join buffer
+2	SUBQUERY	it	ALL	NULL	NULL	NULL	NULL	22	
 select 
 a, mid(filler1, 1,10), length(filler1)=length(filler2) as Z 
 from t1 ot where a in (select a from t2 it);
@@ -225,7 +231,8 @@ a, mid(filler1, 1,10), length(filler1)=length(filler2)
 from t2 ot where a in (select a from t1 it);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	ot	ALL	NULL	NULL	NULL	NULL	22	
-1	PRIMARY	it	ALL	NULL	NULL	NULL	NULL	52	Materialize
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	5	func	1	
+2	SUBQUERY	it	ALL	NULL	NULL	NULL	NULL	52	
 select 
 a, mid(filler1, 1,10), length(filler1)=length(filler2) 
 from t2 ot where a in (select a from t1 it);
@@ -341,7 +348,8 @@ WHERE t1.Code IN (
 SELECT t2.CountryCode FROM t2 WHERE Population > 5000000);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	PRIMARY	NULL	NULL	NULL	31	
-1	PRIMARY	t2	ALL	CountryCode	NULL	NULL	NULL	545	Using where; Materialize
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	3	func	1	
+2	SUBQUERY	t2	ALL	CountryCode	NULL	NULL	NULL	545	Using where
 SELECT Name FROM t1 
 WHERE t1.Code IN (
 SELECT t2.CountryCode FROM t2 WHERE Population > 5000000);
@@ -684,7 +692,8 @@ The following must use loose index scan over t3, key a:
 explain select count(a) from t2 where a in ( SELECT  a FROM t3);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t2	index	a	a	5	NULL	1000	Using index
-1	PRIMARY	t3	index	a	a	5	NULL	30000	Using index; Materialize
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	5	func	1	
+2	SUBQUERY	t3	index	a	a	5	NULL	30000	Using index
 select count(a) from t2 where a in ( SELECT  a FROM t3);
 count(a)
 1000

mysql-test/r/subselect_sj2_jcl6.result

@@ -36,8 +36,9 @@ a	b
 9	5
 explain select * from t2 where b in (select a from t1);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Materialize; Scan
+1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	3	
 1	PRIMARY	t2	ref	b	b	5	test.t1.a	2	Using join buffer
+2	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	3	
 select * from t2 where b in (select a from t1);
 a	b
 1	1
@@ -77,8 +78,9 @@ A.a + 10*B.a, A.a + 10*B.a, A.a + 10*B.a, A.a + 10*B.a
 from t0 A, t0 B where B.a <5;
 explain select * from t3 where b in (select a from t0);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t0	ALL	NULL	NULL	NULL	NULL	10	Materialize; Scan
+1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	10	
 1	PRIMARY	t3	ref	b	b	5	test.t0.a	1	Using join buffer
+2	SUBQUERY	t0	ALL	NULL	NULL	NULL	NULL	10	
 set @save_ecp= @@engine_condition_pushdown;
 set engine_condition_pushdown=0;
 select * from t3 where b in (select A.a+B.a from t0 A, t0 B where B.a<5);
@@ -103,7 +105,8 @@ set max_heap_table_size= @save_max_heap_table_size;
 explain select * from t1 where a in (select b from t2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	
-1	PRIMARY	t2	index	b	b	5	NULL	10	Using index; Materialize
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	5	func	1	
+2	SUBQUERY	t2	index	b	b	5	NULL	10	Using index
 select * from t1;
 a	b
 1	1
@@ -130,8 +133,9 @@ explain select
 a, mid(filler1, 1,10), length(filler1)=length(filler2) as Z 
 from t1 ot where a in (select a from t2 it);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	it	ALL	NULL	NULL	NULL	NULL	22	Materialize; Scan
+1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	22	
 1	PRIMARY	ot	ALL	NULL	NULL	NULL	NULL	32	Using where; Using join buffer
+2	SUBQUERY	it	ALL	NULL	NULL	NULL	NULL	22	
 select 
 a, mid(filler1, 1,10), length(filler1)=length(filler2) as Z 
 from t1 ot where a in (select a from t2 it);
@@ -163,7 +167,8 @@ a, mid(filler1, 1,10), length(filler1)=length(filler2)
 from t2 ot where a in (select a from t1 it);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	ot	ALL	NULL	NULL	NULL	NULL	22	
-1	PRIMARY	it	ALL	NULL	NULL	NULL	NULL	32	Materialize
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	5	func	1	
+2	SUBQUERY	it	ALL	NULL	NULL	NULL	NULL	32	
 select 
 a, mid(filler1, 1,10), length(filler1)=length(filler2) 
 from t2 ot where a in (select a from t1 it);
@@ -196,8 +201,9 @@ explain select
 a, mid(filler1, 1,10), length(filler1)=length(filler2) as Z 
 from t1 ot where a in (select a from t2 it);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	it	ALL	NULL	NULL	NULL	NULL	22	Materialize; Scan
+1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	22	
 1	PRIMARY	ot	ALL	NULL	NULL	NULL	NULL	52	Using where; Using join buffer
+2	SUBQUERY	it	ALL	NULL	NULL	NULL	NULL	22	
 select 
 a, mid(filler1, 1,10), length(filler1)=length(filler2) as Z 
 from t1 ot where a in (select a from t2 it);
@@ -229,7 +235,8 @@ a, mid(filler1, 1,10), length(filler1)=length(filler2)
 from t2 ot where a in (select a from t1 it);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	ot	ALL	NULL	NULL	NULL	NULL	22	
-1	PRIMARY	it	ALL	NULL	NULL	NULL	NULL	52	Materialize
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	5	func	1	
+2	SUBQUERY	it	ALL	NULL	NULL	NULL	NULL	52	
 select 
 a, mid(filler1, 1,10), length(filler1)=length(filler2) 
 from t2 ot where a in (select a from t1 it);
@@ -345,7 +352,8 @@ WHERE t1.Code IN (
 SELECT t2.CountryCode FROM t2 WHERE Population > 5000000);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	PRIMARY	NULL	NULL	NULL	31	
-1	PRIMARY	t2	ALL	CountryCode	NULL	NULL	NULL	545	Using where; Materialize
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	3	func	1	
+2	SUBQUERY	t2	ALL	CountryCode	NULL	NULL	NULL	545	Using where
 SELECT Name FROM t1 
 WHERE t1.Code IN (
 SELECT t2.CountryCode FROM t2 WHERE Population > 5000000);
@@ -690,7 +698,8 @@ The following must use loose index scan over t3, key a:
 explain select count(a) from t2 where a in ( SELECT  a FROM t3);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t2	index	a	a	5	NULL	1000	Using index
-1	PRIMARY	t3	index	a	a	5	NULL	30000	Using index; Materialize
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	5	func	1	
+2	SUBQUERY	t3	index	a	a	5	NULL	30000	Using index
 select count(a) from t2 where a in ( SELECT  a FROM t3);
 count(a)
 1000

mysql-test/r/subselect_sj_jcl6.result

@@ -852,7 +852,8 @@ INSERT INTO t2 VALUES (1,'i','iiii','iiii','iiii','iiii','ffff','ffff','ffff','f
 EXPLAIN EXTENDED SELECT pk FROM t1 WHERE (a, b) IN (SELECT a, b FROM t2 WHERE pk > 0);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	
-1	PRIMARY	t2	range	PRIMARY	PRIMARY	4	NULL	2	100.00	Using index condition; Using MRR; Materialize
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	13	func	1	1.00	
+2	SUBQUERY	t2	range	PRIMARY	PRIMARY	4	NULL	2	100.00	Using index condition; Using MRR
 Warnings:
 Note	1003	select `test`.`t1`.`pk` AS `pk` from `test`.`t1` semi join (`test`.`t2`) where ((`test`.`t2`.`pk` > 0))
 SELECT pk FROM t1 WHERE (a, b) IN (SELECT a, b FROM t2 WHERE pk > 0);
@@ -1020,7 +1021,8 @@ FROM t1
 WHERE `varchar_nokey`  < 'n' XOR `pk`  )   ;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	18	100.00	
-1	PRIMARY	t1	ALL	varchar_key	NULL	NULL	NULL	15	100.00	Using where; Materialize
+1	PRIMARY	subselect2	eq_ref	unique_key	unique_key	8	func	1	1.00	
+2	SUBQUERY	t1	ALL	varchar_key	NULL	NULL	NULL	15	100.00	Using where
 Warnings:
 Note	1003	select `test`.`t2`.`varchar_nokey` AS `varchar_nokey` from `test`.`t2` semi join (`test`.`t1`) where ((`test`.`t1`.`varchar_nokey` = `test`.`t1`.`varchar_key`) and ((`test`.`t1`.`varchar_nokey` < 'n') xor `test`.`t1`.`pk`))
 SELECT varchar_nokey

sql/item_subselect.cc

@@ -926,6 +926,11 @@ Item_in_subselect::Item_in_subselect(Item * left_exp,
   DBUG_VOID_RETURN;
 }
 
+int Item_in_subselect::get_identifier()
+{
+  return engine->get_identifier();
+}
+
 Item_allany_subselect::Item_allany_subselect(Item * left_exp,
                                              chooser_compare_func_creator fc,
 					     st_select_lex *select_lex,
@@ -2271,6 +2276,10 @@ subselect_single_select_engine(st_select_lex *select,
   select_lex->master_unit()->item= item_arg;
 }
 
+int subselect_single_select_engine::get_identifier()
+{
+  return select_lex->select_number; 
+}
 
 void subselect_single_select_engine::cleanup()
 {

sql/item_subselect.h

@@ -433,7 +433,12 @@ class Item_in_subselect :public Item_exists_subselect
   /* Inform 'this' that it was computed, and contains a valid result. */
   void set_first_execution() { if (first_execution) first_execution= FALSE; }
   bool is_expensive_processor(uchar *arg);
-
+  
+  /* 
+    Return the identifier that we could use to identify the subquery for the
+    user.
+  */
+  int get_identifier();
   friend class Item_ref_null_helper;
   friend class Item_is_not_null_test;
   friend class Item_in_optimizer;
@@ -534,7 +539,7 @@ class subselect_engine: public Sql_alloc
   /* Check if subquery produced any rows during last query execution */
   virtual bool no_rows() = 0;
   virtual enum_engine_type engine_type() { return ABSTRACT_ENGINE; }
-
+  virtual int get_identifier() { DBUG_ASSERT(0); return 0; }
 protected:
   void set_row(List<Item> &item_list, Item_cache **row);
 };
@@ -566,6 +571,7 @@ class subselect_single_select_engine: public subselect_engine
   bool is_executed() const { return executed; }
   bool no_rows();
   virtual enum_engine_type engine_type() { return SINGLE_SELECT_ENGINE; }
+  int get_identifier();
 
   friend class subselect_hash_sj_engine;
   friend class Item_in_subselect;

sql/sql_select.cc

@@ -17889,8 +17889,15 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
   else
   {
     table_map used_tables=0;
-    uint last_sjm_table= MAX_TABLES;
-    for (uint i=0 ; i < join->tables ; i++)
+
+    uchar sjm_nests[MAX_TABLES];
+    uint sjm_nests_cur=0;
+    uint sjm_nests_end= 0;
+    uint end_table= join->tables;
+    bool printing_materialize_nest= FALSE;
+    uint select_id= join->select_lex->select_number;
+
+    for (uint i=0 ; i < end_table ; i++)
     {
       JOIN_TAB *tab=join->join_tab+i;
       TABLE *table=tab->table;
@@ -17898,6 +17905,7 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
       char buff[512]; 
       char buff1[512], buff2[512], buff3[512];
       char keylen_str_buf[64];
+      my_bool key_read;
       String extra(buff, sizeof(buff),cs);
       char table_name_buffer[NAME_LEN];
       String tmp1(buff1,sizeof(buff1),cs);
@@ -17907,7 +17915,6 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
       tmp1.length(0);
       tmp2.length(0);
       tmp3.length(0);
-
       quick_type= -1;
 
       /* Don't show eliminated tables */
@@ -17919,12 +17926,89 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
 
       item_list.empty();
       /* id */
-      item_list.push_back(new Item_uint((uint32)
-				       join->select_lex->select_number));
+      item_list.push_back(new Item_uint((uint32)select_id));
       /* select_type */
-      item_list.push_back(new Item_string(join->select_lex->type,
-					  strlen(join->select_lex->type),
-					  cs));
+      const char* stype= printing_materialize_nest? "SUBQUERY" : 
+                                                    join->select_lex->type;
+      item_list.push_back(new Item_string(stype, strlen(stype), cs));
+      
+      /* 
+        Special processing for SJ-Materialization nests: print the fake table
+        and delay printing of the SJM nest contents until later.
+      */
+      uint sj_strategy= join->best_positions[i].sj_strategy;
+      if (sj_is_materialize_strategy(sj_strategy) &&
+          !printing_materialize_nest)
+      {
+        /* table */
+        int len= my_snprintf(table_name_buffer, 
+                             sizeof(table_name_buffer)-1,
+                             "subselect%d", 
+                             tab->emb_sj_nest->sj_subq_pred->get_identifier());
+	item_list.push_back(new Item_string(table_name_buffer, len, cs));
+        /* partitions */
+        if (join->thd->lex->describe & DESCRIBE_PARTITIONS)
+          item_list.push_back(item_null);
+        /* type */
+        uint type= (sj_strategy == SJ_OPT_MATERIALIZE_SCAN)? JT_ALL : JT_EQ_REF;
+        item_list.push_back(new Item_string(join_type_str[type],
+                                            strlen(join_type_str[type]),
+                                            cs));
+        /* possible_keys */
+	item_list.push_back(new Item_string("unique_key", 
+                                            strlen("unique_key"), cs));
+        if (sj_strategy == SJ_OPT_MATERIALIZE_SCAN)
+        {
+          item_list.push_back(item_null); /* key */
+          item_list.push_back(item_null); /* key_len */
+          item_list.push_back(item_null); /* ref */
+        }
+        else
+        {
+          /* key */
+          item_list.push_back(new Item_string("unique_key", strlen("unique_key"), cs));
+          /* key_len */
+          uint klen= tab->emb_sj_nest->sj_mat_info->table->key_info[0].key_length;
+          uint buflen= longlong2str(klen, keylen_str_buf, 10) - keylen_str_buf;
+          item_list.push_back(new Item_string(keylen_str_buf, buflen, cs));
+          /* ref */
+          item_list.push_back(new Item_string("func", strlen("func"), cs));
+        }
+        /* rows */
+        ha_rows rows= (sj_strategy == SJ_OPT_MATERIALIZE_SCAN)?
+                       tab->emb_sj_nest->sj_mat_info->rows : 1;
+        item_list.push_back(new Item_int(rows));
+        /* filtered */
+        if (join->thd->lex->describe & DESCRIBE_EXTENDED)
+          item_list.push_back(new Item_float(1.0, 2));
+        
+        /* Extra */
+	if (need_tmp_table)
+	{
+	  need_tmp_table=0;
+	  extra.append(STRING_WITH_LEN("; Using temporary"));
+	}
+	if (need_order)
+	{
+	  need_order=0;
+	  extra.append(STRING_WITH_LEN("; Using filesort"));
+	}
+        /* Skip initial "; "*/
+        const char *str= extra.ptr();
+        uint32 extra_len= extra.length();
+        if (extra_len)
+        {
+          str += 2;
+          extra_len -= 2;
+        }
+	item_list.push_back(new Item_string(str, extra_len, cs));
+
+        /* Register the nest for further processing: */
+        sjm_nests[sjm_nests_end++]= i;
+        i += join->best_positions[i].n_sj_tables-1;
+        goto loop_end;
+      }
+
       if (tab->type == JT_ALL && tab->select && tab->select->quick)
       {
         quick_type= tab->select->quick->get_type();
@@ -17935,6 +18019,7 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
         else
 	  tab->type = JT_RANGE;
       }
+
       /* table */
       if (table->derived_select_number)
       {
@@ -18113,7 +18198,7 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
       }
 
       /* Build "Extra" field and add it to item_list. */
-      my_bool key_read=table->key_read;
+      key_read=table->key_read;
       if ((tab->type == JT_NEXT || tab->type == JT_CONST) &&
           table->covering_keys.is_set(tab->index))
 	key_read=1;
@@ -18269,7 +18354,8 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
             extra.append(STRING_WITH_LEN(")"));
           }
         }
-        uint sj_strategy= join->best_positions[i].sj_strategy;
+
+        /*
         if (sj_is_materialize_strategy(sj_strategy))
         {
           if (join->best_positions[i].n_sj_tables == 1)
@@ -18286,6 +18372,7 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
         {
           extra.append(STRING_WITH_LEN("; End materialize"));
         }
+        */
 
         for (uint part= 0; part < tab->ref.key_parts; part++)
         {
@@ -18309,6 +18396,15 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
         }
 	item_list.push_back(new Item_string(str, len, cs));
       }
+    loop_end:
+       if (i+1 == end_table && sjm_nests_cur != sjm_nests_end)
+       {
+         printing_materialize_nest= TRUE;
+         i= sjm_nests[sjm_nests_cur++] - 1;
+         end_table= (i+1) + join->best_positions[i+1].n_sj_tables;
+         select_id= join->join_tab[i+1].emb_sj_nest->sj_subq_pred->get_identifier();
+       }
+      
       // For next iteration
       used_tables|=table->map;
       if (result->send_data(item_list))