Fix for MDEV-4144

  
Analysis:
The reason for the inefficent plan was that Item_subselect::is_expensive()
didn't detect the special case when a subquery was optimized, but had no
join plan because it either has no table, or its tables have been optimized
away, or the optimizer detected that the result set is empty.
  
Solution:
Identify the special cases above in the Item_subselect::is_expensive(),
and consider such degenerate subqueries inexpensive.

1 files changed, 19 insertions, 5 deletions

diff --git a/mysql-test/r/subselect4.result b/mysql-test/r/subselect4.result
index 2814e5a6dcd..11b27e76782 100644
--- a/mysql-test/r/subselect4.result
+++ b/mysql-test/r/subselect4.result
@@ -869,7 +869,7 @@ NULL
 EXPLAIN
 SELECT * FROM t1 WHERE (2, 0) NOT IN (SELECT min(f3)+f3, min(f4)+f3+max(f4) FROM t2);
 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	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
 2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No matching min/max row
 SELECT * FROM t1 WHERE (2, 0) NOT IN (SELECT min(f3)+f3, min(f4)+f3+max(f4) FROM t2);
 f1	f2
@@ -960,7 +960,7 @@ NULL
 EXPLAIN
 SELECT * FROM t1 WHERE (2, 0) NOT IN (SELECT min(f3)+f3, min(f4)+f3+max(f4) FROM t2);
 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	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
 2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No matching min/max row
 SELECT * FROM t1 WHERE (2, 0) NOT IN (SELECT min(f3)+f3, min(f4)+f3+max(f4) FROM t2);
 f1	f2
@@ -1055,7 +1055,7 @@ NULL
 EXPLAIN
 SELECT * FROM t1 WHERE (2, 0) NOT IN (SELECT min(f3)+f3, min(f4)+f3+max(f4) FROM t2 WHERE f3 > 10);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	2	
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
 2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No matching min/max row
 SELECT * FROM t1 WHERE (2, 0) NOT IN (SELECT min(f3)+f3, min(f4)+f3+max(f4) FROM t2 WHERE f3 > 10);
 f1	f2
@@ -1146,7 +1146,7 @@ NULL
 EXPLAIN
 SELECT * FROM t1 WHERE (2, 0) NOT IN (SELECT min(f3)+f3, min(f4)+f3+max(f4) FROM t2 WHERE f3 > 10);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	2	
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
 2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No matching min/max row
 SELECT * FROM t1 WHERE (2, 0) NOT IN (SELECT min(f3)+f3, min(f4)+f3+max(f4) FROM t2 WHERE f3 > 10);
 f1	f2
@@ -2012,7 +2012,7 @@ FROM t2 JOIN t3 ON t3.f4 = t2.f4
 WHERE t3.f1 = 8
 GROUP BY 1, 2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t3	system	NULL	NULL	NULL	NULL	1	Using temporary; Using filesort
+1	PRIMARY	t3	system	NULL	NULL	NULL	NULL	1	Using filesort
 1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	2	Using where
 2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
 3	MATERIALIZED	NULL	NULL	NULL	NULL	NULL	NULL	NULL	no matching row in const table
@@ -2325,5 +2325,19 @@ ORDER BY alias1.b;
 pk	b	pk	b
 1	1	1	1
 drop table t1, t2, t3;
+#
+# MDEV-4144 simple subquery causes full scan instead of range scan
+#
+CREATE TABLE t1 (id int not null auto_increment, x int not null, primary key(id));
+INSERT INTO t1 (x) VALUES (0),(0),(0);
+EXPLAIN
+SELECT x FROM t1 WHERE id > (SELECT MAX(id) - 1000 FROM t1) ORDER BY x LIMIT 1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	range	PRIMARY	PRIMARY	4	NULL	3	Using where; Using filesort
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+SELECT x FROM t1 WHERE id > (SELECT MAX(id) - 1000 FROM t1) ORDER BY x LIMIT 1;
+x
+0
+drop table t1;
 SET optimizer_switch= @@global.optimizer_switch;
 set @@tmp_table_size= @@global.tmp_table_size;