MDEV-410: EXPLAIN shows type=range, while SHOW EXPLAIN and userstat show full table scan is used

- Make Item_subselect::fix_fields() ignore UNCACHEABLE_EXPLAIN flag when deciding whether 
  the subquery item should be marked as constant.

mysql-test/r/func_group.result

@@ -1838,7 +1838,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	PRIMARY	t1	range	a	a	4	NULL	4	100.00	Using where; Using index
 2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
 Warnings:
-Note	1003	select max(`test`.`t1`.`a`) AS `MAX(a)` from `test`.`t1` where (<expr_cache><<cache>(1),<cache>(2)>(<in_optimizer>(<cache>((1,2)),<exists>(select 3,4 having (((1 = 3) or isnull(3)) and ((2 = 4) or isnull(4)) and <is_not_null_test>(3) and <is_not_null_test>(4))))) and (`test`.`t1`.`a` < 10))
+Note	1003	select max(`test`.`t1`.`a`) AS `MAX(a)` from `test`.`t1` where (<cache>(<in_optimizer>((1,2),<exists>(select 3,4 having (((1 = 3) or isnull(3)) and ((2 = 4) or isnull(4)) and <is_not_null_test>(3) and <is_not_null_test>(4))))) and (`test`.`t1`.`a` < 10))
 SELECT MAX(a) FROM t1 WHERE (1,2) IN (SELECT 3,4) AND a<10;
 MAX(a)
 NULL

mysql-test/r/subselect.result

@@ -6768,5 +6768,43 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 SELECT * FROM t1 WHERE 4 IN (SELECT MAX(b) FROM t2 WHERE EXISTS (SELECT * FROM t1));
 a
 drop table t1,t2;
+#
+# MDEV-410: EXPLAIN shows type=range, while SHOW EXPLAIN and userstat show full table scan is used
+#
+CREATE TABLE t1 (a VARCHAR(3) PRIMARY KEY) ENGINE=MyISAM;
+INSERT INTO t1 VALUES ('USA');
+CREATE TABLE t2 (b INT, c VARCHAR(52), KEY(b)) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (3813,'United States'),(3940,'Russia');
+CREATE TABLE t3 (d INT, KEY(d)) ENGINE=MyISAM;
+INSERT INTO t3 VALUES (12),(22),(9),(45);
+create table t4 like t3;
+insert into t4 select * from t3;
+# This should not show range access for table t2
+explain
+SELECT MIN(b) FROM ( SELECT * FROM t1, t2, t3 WHERE d = b ) AS alias1 
+WHERE SLEEP(0.1) OR c < 'p' OR b = ( SELECT MIN(b) FROM t2 );
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	system	NULL	NULL	NULL	NULL	1	
+1	PRIMARY	t2	ALL	b	NULL	NULL	NULL	2	Using where
+1	PRIMARY	t3	ref	d	d	5	test.t2.b	2	Using where; Using index
+3	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+set @tmp_mdev410=@@global.userstat;
+set global userstat=on;
+flush table_statistics;
+flush index_statistics;
+SELECT MIN(b) FROM ( SELECT * FROM t1, t2, t3 WHERE d = b ) AS alias1 
+WHERE SLEEP(0.1) OR c < 'p' OR b = ( SELECT MIN(b) FROM t2 );
+MIN(b)
+NULL
+# The following shows that t2 was indeed scanned with a full scan.
+show table_statistics;
+Table_schema	Table_name	Rows_read	Rows_changed	Rows_changed_x_#indexes
+test	t1	2	0	0
+test	t2	3	0	0
+show index_statistics;
+Table_schema	Table_name	Index_name	Rows_read
+test	t2	b	1
+set global userstat=@tmp_mdev410;
+DROP TABLE t1,t2,t3,t4;
 # return optimizer switch changed in the beginning of this test
 set optimizer_switch=@subselect_tmp;

mysql-test/r/subselect2.result

@@ -161,18 +161,18 @@ SET optimizer_switch='materialization=on,in_to_exists=on';
 EXPLAIN
 SELECT * FROM t2,t3 WHERE (2,9) IN (SELECT DISTINCT a,pk FROM t1) OR a = b;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t2	index	a	a	5	NULL	2	Using index
-1	PRIMARY	t3	index	b	b	5	NULL	4	Using where; Using index; Using join buffer (flat, BNL join)
-2	MATERIALIZED	t1	index	PRIMARY,a	a	5	NULL	2	Using index
+1	PRIMARY	t2	index	a	a	5	NULL	2	Using where; Using index
+1	PRIMARY	t3	ref	b	b	5	test.t2.a	2	Using index
+2	SUBQUERY	t1	index_subquery	PRIMARY,a	a	5	const	0	Using index; Using where
 SELECT * FROM t2,t3 WHERE (2,9) IN (SELECT DISTINCT a,pk FROM t1) OR a = b;
 pk	a	b
 0	4	4
 EXPLAIN
 SELECT * FROM t2,t3 WHERE (2,9) IN (SELECT DISTINCT a,pk FROM v1) OR a = b;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t2	index	a	a	5	NULL	2	Using index
-1	PRIMARY	t3	index	b	b	5	NULL	4	Using where; Using index; Using join buffer (flat, BNL join)
-2	MATERIALIZED	t1	index	PRIMARY,a	a	5	NULL	2	Using index
+1	PRIMARY	t2	index	a	a	5	NULL	2	Using where; Using index
+1	PRIMARY	t3	ref	b	b	5	test.t2.a	2	Using index
+2	SUBQUERY	t1	index_subquery	PRIMARY,a	a	5	const	0	Using index; Using where
 SELECT * FROM t2,t3 WHERE (2,9) IN (SELECT DISTINCT a,pk FROM v1) OR a = b;
 pk	a	b
 0	4	4

mysql-test/r/subselect_mat.result

@@ -2183,7 +2183,7 @@ NULL
 EXPLAIN
 SELECT * FROM t2 WHERE (SELECT f3a, f3b FROM t3) NOT IN (SELECT f1a, f1b FROM t1);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	2	
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
 3	MATERIALIZED	t1	ALL	NULL	NULL	NULL	NULL	2	
 2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	no matching row in const table
 SELECT * FROM t2 WHERE (SELECT f3a, f3b FROM t3) NOT IN (SELECT f1a, f1b FROM t1);

mysql-test/r/subselect_mat_cost_bugs.result

@@ -162,7 +162,7 @@ EXPLAIN
 SELECT * FROM (SELECT * FROM t2) AS a2
 WHERE (SELECT distinct SUM(distinct f3 ) FROM t1);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+1	PRIMARY	<derived2>	system	NULL	NULL	NULL	NULL	0	const row not found
 3	SUBQUERY	t1	index	NULL	f3	5	NULL	2	Using index
 2	DERIVED	NULL	NULL	NULL	NULL	NULL	NULL	NULL	no matching row in const table
 insert into t2 values (1),(2);

mysql-test/r/subselect_no_mat.result

@@ -6766,6 +6766,44 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 SELECT * FROM t1 WHERE 4 IN (SELECT MAX(b) FROM t2 WHERE EXISTS (SELECT * FROM t1));
 a
 drop table t1,t2;
+#
+# MDEV-410: EXPLAIN shows type=range, while SHOW EXPLAIN and userstat show full table scan is used
+#
+CREATE TABLE t1 (a VARCHAR(3) PRIMARY KEY) ENGINE=MyISAM;
+INSERT INTO t1 VALUES ('USA');
+CREATE TABLE t2 (b INT, c VARCHAR(52), KEY(b)) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (3813,'United States'),(3940,'Russia');
+CREATE TABLE t3 (d INT, KEY(d)) ENGINE=MyISAM;
+INSERT INTO t3 VALUES (12),(22),(9),(45);
+create table t4 like t3;
+insert into t4 select * from t3;
+# This should not show range access for table t2
+explain
+SELECT MIN(b) FROM ( SELECT * FROM t1, t2, t3 WHERE d = b ) AS alias1 
+WHERE SLEEP(0.1) OR c < 'p' OR b = ( SELECT MIN(b) FROM t2 );
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	system	NULL	NULL	NULL	NULL	1	
+1	PRIMARY	t2	ALL	b	NULL	NULL	NULL	2	Using where
+1	PRIMARY	t3	ref	d	d	5	test.t2.b	2	Using where; Using index
+3	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+set @tmp_mdev410=@@global.userstat;
+set global userstat=on;
+flush table_statistics;
+flush index_statistics;
+SELECT MIN(b) FROM ( SELECT * FROM t1, t2, t3 WHERE d = b ) AS alias1 
+WHERE SLEEP(0.1) OR c < 'p' OR b = ( SELECT MIN(b) FROM t2 );
+MIN(b)
+NULL
+# The following shows that t2 was indeed scanned with a full scan.
+show table_statistics;
+Table_schema	Table_name	Rows_read	Rows_changed	Rows_changed_x_#indexes
+test	t1	2	0	0
+test	t2	3	0	0
+show index_statistics;
+Table_schema	Table_name	Index_name	Rows_read
+test	t2	b	1
+set global userstat=@tmp_mdev410;
+DROP TABLE t1,t2,t3,t4;
 # return optimizer switch changed in the beginning of this test
 set optimizer_switch=@subselect_tmp;
 set optimizer_switch=default;

mysql-test/r/subselect_no_opts.result

@@ -6763,6 +6763,44 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 SELECT * FROM t1 WHERE 4 IN (SELECT MAX(b) FROM t2 WHERE EXISTS (SELECT * FROM t1));
 a
 drop table t1,t2;
+#
+# MDEV-410: EXPLAIN shows type=range, while SHOW EXPLAIN and userstat show full table scan is used
+#
+CREATE TABLE t1 (a VARCHAR(3) PRIMARY KEY) ENGINE=MyISAM;
+INSERT INTO t1 VALUES ('USA');
+CREATE TABLE t2 (b INT, c VARCHAR(52), KEY(b)) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (3813,'United States'),(3940,'Russia');
+CREATE TABLE t3 (d INT, KEY(d)) ENGINE=MyISAM;
+INSERT INTO t3 VALUES (12),(22),(9),(45);
+create table t4 like t3;
+insert into t4 select * from t3;
+# This should not show range access for table t2
+explain
+SELECT MIN(b) FROM ( SELECT * FROM t1, t2, t3 WHERE d = b ) AS alias1 
+WHERE SLEEP(0.1) OR c < 'p' OR b = ( SELECT MIN(b) FROM t2 );
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	system	NULL	NULL	NULL	NULL	1	
+1	PRIMARY	t2	ALL	b	NULL	NULL	NULL	2	Using where
+1	PRIMARY	t3	ref	d	d	5	test.t2.b	2	Using where; Using index
+3	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+set @tmp_mdev410=@@global.userstat;
+set global userstat=on;
+flush table_statistics;
+flush index_statistics;
+SELECT MIN(b) FROM ( SELECT * FROM t1, t2, t3 WHERE d = b ) AS alias1 
+WHERE SLEEP(0.1) OR c < 'p' OR b = ( SELECT MIN(b) FROM t2 );
+MIN(b)
+NULL
+# The following shows that t2 was indeed scanned with a full scan.
+show table_statistics;
+Table_schema	Table_name	Rows_read	Rows_changed	Rows_changed_x_#indexes
+test	t1	2	0	0
+test	t2	3	0	0
+show index_statistics;
+Table_schema	Table_name	Index_name	Rows_read
+test	t2	b	1
+set global userstat=@tmp_mdev410;
+DROP TABLE t1,t2,t3,t4;
 # return optimizer switch changed in the beginning of this test
 set optimizer_switch=@subselect_tmp;
 set @optimizer_switch_for_subselect_test=null;

mysql-test/r/subselect_no_scache.result

@@ -6774,6 +6774,44 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 SELECT * FROM t1 WHERE 4 IN (SELECT MAX(b) FROM t2 WHERE EXISTS (SELECT * FROM t1));
 a
 drop table t1,t2;
+#
+# MDEV-410: EXPLAIN shows type=range, while SHOW EXPLAIN and userstat show full table scan is used
+#
+CREATE TABLE t1 (a VARCHAR(3) PRIMARY KEY) ENGINE=MyISAM;
+INSERT INTO t1 VALUES ('USA');
+CREATE TABLE t2 (b INT, c VARCHAR(52), KEY(b)) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (3813,'United States'),(3940,'Russia');
+CREATE TABLE t3 (d INT, KEY(d)) ENGINE=MyISAM;
+INSERT INTO t3 VALUES (12),(22),(9),(45);
+create table t4 like t3;
+insert into t4 select * from t3;
+# This should not show range access for table t2
+explain
+SELECT MIN(b) FROM ( SELECT * FROM t1, t2, t3 WHERE d = b ) AS alias1 
+WHERE SLEEP(0.1) OR c < 'p' OR b = ( SELECT MIN(b) FROM t2 );
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	system	NULL	NULL	NULL	NULL	1	
+1	PRIMARY	t2	ALL	b	NULL	NULL	NULL	2	Using where
+1	PRIMARY	t3	ref	d	d	5	test.t2.b	2	Using where; Using index
+3	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+set @tmp_mdev410=@@global.userstat;
+set global userstat=on;
+flush table_statistics;
+flush index_statistics;
+SELECT MIN(b) FROM ( SELECT * FROM t1, t2, t3 WHERE d = b ) AS alias1 
+WHERE SLEEP(0.1) OR c < 'p' OR b = ( SELECT MIN(b) FROM t2 );
+MIN(b)
+NULL
+# The following shows that t2 was indeed scanned with a full scan.
+show table_statistics;
+Table_schema	Table_name	Rows_read	Rows_changed	Rows_changed_x_#indexes
+test	t1	2	0	0
+test	t2	3	0	0
+show index_statistics;
+Table_schema	Table_name	Index_name	Rows_read
+test	t2	b	1
+set global userstat=@tmp_mdev410;
+DROP TABLE t1,t2,t3,t4;
 # return optimizer switch changed in the beginning of this test
 set optimizer_switch=@subselect_tmp;
 set optimizer_switch=default;

mysql-test/r/subselect_no_semijoin.result

@@ -6763,6 +6763,44 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 SELECT * FROM t1 WHERE 4 IN (SELECT MAX(b) FROM t2 WHERE EXISTS (SELECT * FROM t1));
 a
 drop table t1,t2;
+#
+# MDEV-410: EXPLAIN shows type=range, while SHOW EXPLAIN and userstat show full table scan is used
+#
+CREATE TABLE t1 (a VARCHAR(3) PRIMARY KEY) ENGINE=MyISAM;
+INSERT INTO t1 VALUES ('USA');
+CREATE TABLE t2 (b INT, c VARCHAR(52), KEY(b)) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (3813,'United States'),(3940,'Russia');
+CREATE TABLE t3 (d INT, KEY(d)) ENGINE=MyISAM;
+INSERT INTO t3 VALUES (12),(22),(9),(45);
+create table t4 like t3;
+insert into t4 select * from t3;
+# This should not show range access for table t2
+explain
+SELECT MIN(b) FROM ( SELECT * FROM t1, t2, t3 WHERE d = b ) AS alias1 
+WHERE SLEEP(0.1) OR c < 'p' OR b = ( SELECT MIN(b) FROM t2 );
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	system	NULL	NULL	NULL	NULL	1	
+1	PRIMARY	t2	ALL	b	NULL	NULL	NULL	2	Using where
+1	PRIMARY	t3	ref	d	d	5	test.t2.b	2	Using where; Using index
+3	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+set @tmp_mdev410=@@global.userstat;
+set global userstat=on;
+flush table_statistics;
+flush index_statistics;
+SELECT MIN(b) FROM ( SELECT * FROM t1, t2, t3 WHERE d = b ) AS alias1 
+WHERE SLEEP(0.1) OR c < 'p' OR b = ( SELECT MIN(b) FROM t2 );
+MIN(b)
+NULL
+# The following shows that t2 was indeed scanned with a full scan.
+show table_statistics;
+Table_schema	Table_name	Rows_read	Rows_changed	Rows_changed_x_#indexes
+test	t1	2	0	0
+test	t2	3	0	0
+show index_statistics;
+Table_schema	Table_name	Index_name	Rows_read
+test	t2	b	1
+set global userstat=@tmp_mdev410;
+DROP TABLE t1,t2,t3,t4;
 # return optimizer switch changed in the beginning of this test
 set optimizer_switch=@subselect_tmp;
 set @optimizer_switch_for_subselect_test=null;

mysql-test/t/subselect.test

@@ -5686,5 +5686,40 @@ SELECT * FROM t1 WHERE 4 IN (SELECT MAX(b) FROM t2 WHERE EXISTS (SELECT * FROM t
 drop table t1,t2;
 
 
+--echo #
+--echo # MDEV-410: EXPLAIN shows type=range, while SHOW EXPLAIN and userstat show full table scan is used
+--echo #
+CREATE TABLE t1 (a VARCHAR(3) PRIMARY KEY) ENGINE=MyISAM;
+INSERT INTO t1 VALUES ('USA');
+
+CREATE TABLE t2 (b INT, c VARCHAR(52), KEY(b)) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (3813,'United States'),(3940,'Russia');
+
+CREATE TABLE t3 (d INT, KEY(d)) ENGINE=MyISAM;
+INSERT INTO t3 VALUES (12),(22),(9),(45);
+
+create table t4 like t3;
+insert into t4 select * from t3;
+
+--echo # This should not show range access for table t2
+explain
+SELECT MIN(b) FROM ( SELECT * FROM t1, t2, t3 WHERE d = b ) AS alias1 
+WHERE SLEEP(0.1) OR c < 'p' OR b = ( SELECT MIN(b) FROM t2 );
+
+set @tmp_mdev410=@@global.userstat;
+set global userstat=on;
+flush table_statistics;
+flush index_statistics;
+
+SELECT MIN(b) FROM ( SELECT * FROM t1, t2, t3 WHERE d = b ) AS alias1 
+WHERE SLEEP(0.1) OR c < 'p' OR b = ( SELECT MIN(b) FROM t2 );
+
+--echo # The following shows that t2 was indeed scanned with a full scan.
+show table_statistics;
+show index_statistics;
+set global userstat=@tmp_mdev410;
+
+DROP TABLE t1,t2,t3,t4;
+
 --echo # return optimizer switch changed in the beginning of this test
 set optimizer_switch=@subselect_tmp;

sql/item_subselect.cc

@@ -287,7 +287,7 @@ bool Item_subselect::fix_fields(THD *thd_param, Item **ref)
   else
     goto end;
   
-  if ((uncacheable= engine->uncacheable()))
+  if ((uncacheable= engine->uncacheable() & ~UNCACHEABLE_EXPLAIN))
   {
     const_item_cache= 0;
     if (uncacheable & UNCACHEABLE_RAND)