From 1fde449f1d4e8ebe12e989754bfdc84b123cf0b2 Mon Sep 17 00:00:00 2001
From: Igor Babaev <igor@askmonty.org>
Date: Tue, 24 Jul 2018 23:45:55 -0700
Subject: [PATCH] MDEV-16820 Lost 'Impossible where' from query with
 inexpensive subquery

This patch fixes another problem introduced by the patch for mdev-4817.
The latter changed Item_cond::fix_fields() in such a way that it could
call the virtual method is_expensive(). With the first its call
the method saves the result in Item::is_expensive_cache. For all next
calls the method returns the result from this cache. So if the item
once was determined as expensive the method always returns true.
For subqueries it's not good, because non-optimized subqueries always
is considered as expensive.
It means that the cache should be invalidated after the call of
optimize_constant_subqueries().
---
 mysql-test/r/subselect.result                 | 16 ++++++++++++++++
 mysql-test/r/subselect_no_exists_to_in.result | 16 ++++++++++++++++
 mysql-test/r/subselect_no_mat.result          | 16 ++++++++++++++++
 mysql-test/r/subselect_no_opts.result         | 16 ++++++++++++++++
 mysql-test/r/subselect_no_scache.result       | 16 ++++++++++++++++
 mysql-test/r/subselect_no_semijoin.result     | 16 ++++++++++++++++
 mysql-test/t/subselect.test                   | 15 +++++++++++++++
 sql/item.h                                    |  5 +++++
 sql/sql_select.cc                             |  7 +++++++
 9 files changed, 123 insertions(+)

diff --git a/mysql-test/r/subselect.result b/mysql-test/r/subselect.result
index 40f936fb3b4..69db0959373 100644
--- a/mysql-test/r/subselect.result
+++ b/mysql-test/r/subselect.result
@@ -7235,6 +7235,22 @@ a
 5
 SET @@optimizer_switch= @optimiser_switch_save;
 DROP TABLE t1, t2, t3;
+#
+# MDEV-16820: impossible where with inexpensive subquery
+#
+create table t1 (a int) engine=myisam;
+insert into t1 values (3), (1), (7);
+create table t2 (b int, index idx(b));
+insert into t2 values (2), (5), (3), (2);
+explain select * from t1 where (select max(b) from t2) = 10;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+explain select * from t1 where (select max(b) from t2) = 10 and t1.a > 3;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+drop table t1,t2;
 End of 5.5 tests
 # End of 10.0 tests
 #
diff --git a/mysql-test/r/subselect_no_exists_to_in.result b/mysql-test/r/subselect_no_exists_to_in.result
index a23820820ef..ef3bf7ef692 100644
--- a/mysql-test/r/subselect_no_exists_to_in.result
+++ b/mysql-test/r/subselect_no_exists_to_in.result
@@ -7235,6 +7235,22 @@ a
 5
 SET @@optimizer_switch= @optimiser_switch_save;
 DROP TABLE t1, t2, t3;
+#
+# MDEV-16820: impossible where with inexpensive subquery
+#
+create table t1 (a int) engine=myisam;
+insert into t1 values (3), (1), (7);
+create table t2 (b int, index idx(b));
+insert into t2 values (2), (5), (3), (2);
+explain select * from t1 where (select max(b) from t2) = 10;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+explain select * from t1 where (select max(b) from t2) = 10 and t1.a > 3;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+drop table t1,t2;
 End of 5.5 tests
 # End of 10.0 tests
 #
diff --git a/mysql-test/r/subselect_no_mat.result b/mysql-test/r/subselect_no_mat.result
index baa74307f89..703572e0ef8 100644
--- a/mysql-test/r/subselect_no_mat.result
+++ b/mysql-test/r/subselect_no_mat.result
@@ -7228,6 +7228,22 @@ a
 5
 SET @@optimizer_switch= @optimiser_switch_save;
 DROP TABLE t1, t2, t3;
+#
+# MDEV-16820: impossible where with inexpensive subquery
+#
+create table t1 (a int) engine=myisam;
+insert into t1 values (3), (1), (7);
+create table t2 (b int, index idx(b));
+insert into t2 values (2), (5), (3), (2);
+explain select * from t1 where (select max(b) from t2) = 10;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+explain select * from t1 where (select max(b) from t2) = 10 and t1.a > 3;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+drop table t1,t2;
 End of 5.5 tests
 # End of 10.0 tests
 #
diff --git a/mysql-test/r/subselect_no_opts.result b/mysql-test/r/subselect_no_opts.result
index 039f2fe1a9e..39a098b754b 100644
--- a/mysql-test/r/subselect_no_opts.result
+++ b/mysql-test/r/subselect_no_opts.result
@@ -7226,6 +7226,22 @@ a
 5
 SET @@optimizer_switch= @optimiser_switch_save;
 DROP TABLE t1, t2, t3;
+#
+# MDEV-16820: impossible where with inexpensive subquery
+#
+create table t1 (a int) engine=myisam;
+insert into t1 values (3), (1), (7);
+create table t2 (b int, index idx(b));
+insert into t2 values (2), (5), (3), (2);
+explain select * from t1 where (select max(b) from t2) = 10;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+explain select * from t1 where (select max(b) from t2) = 10 and t1.a > 3;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+drop table t1,t2;
 End of 5.5 tests
 # End of 10.0 tests
 #
diff --git a/mysql-test/r/subselect_no_scache.result b/mysql-test/r/subselect_no_scache.result
index 0ce77bbb376..b9a59bf3952 100644
--- a/mysql-test/r/subselect_no_scache.result
+++ b/mysql-test/r/subselect_no_scache.result
@@ -7241,6 +7241,22 @@ a
 5
 SET @@optimizer_switch= @optimiser_switch_save;
 DROP TABLE t1, t2, t3;
+#
+# MDEV-16820: impossible where with inexpensive subquery
+#
+create table t1 (a int) engine=myisam;
+insert into t1 values (3), (1), (7);
+create table t2 (b int, index idx(b));
+insert into t2 values (2), (5), (3), (2);
+explain select * from t1 where (select max(b) from t2) = 10;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+explain select * from t1 where (select max(b) from t2) = 10 and t1.a > 3;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+drop table t1,t2;
 End of 5.5 tests
 # End of 10.0 tests
 #
diff --git a/mysql-test/r/subselect_no_semijoin.result b/mysql-test/r/subselect_no_semijoin.result
index 574e78122f1..f1df85fed6e 100644
--- a/mysql-test/r/subselect_no_semijoin.result
+++ b/mysql-test/r/subselect_no_semijoin.result
@@ -7226,6 +7226,22 @@ a
 5
 SET @@optimizer_switch= @optimiser_switch_save;
 DROP TABLE t1, t2, t3;
+#
+# MDEV-16820: impossible where with inexpensive subquery
+#
+create table t1 (a int) engine=myisam;
+insert into t1 values (3), (1), (7);
+create table t2 (b int, index idx(b));
+insert into t2 values (2), (5), (3), (2);
+explain select * from t1 where (select max(b) from t2) = 10;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+explain select * from t1 where (select max(b) from t2) = 10 and t1.a > 3;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+drop table t1,t2;
 End of 5.5 tests
 # End of 10.0 tests
 #
diff --git a/mysql-test/t/subselect.test b/mysql-test/t/subselect.test
index 717871db61d..a4c4c21610e 100644
--- a/mysql-test/t/subselect.test
+++ b/mysql-test/t/subselect.test
@@ -6098,6 +6098,21 @@ and t1.a in (select `test`.`t3`.`c` from `test`.`t3`);
 SET @@optimizer_switch= @optimiser_switch_save;
 DROP TABLE t1, t2, t3;
 
+--echo #
+--echo # MDEV-16820: impossible where with inexpensive subquery
+--echo #
+
+create table t1 (a int) engine=myisam;
+insert into t1 values (3), (1), (7);
+
+create table t2 (b int, index idx(b));
+insert into t2 values (2), (5), (3), (2);
+
+explain select * from t1 where (select max(b) from t2) = 10;
+explain select * from t1 where (select max(b) from t2) = 10 and t1.a > 3;
+
+drop table t1,t2;
+
 --echo End of 5.5 tests
 --echo # End of 10.0 tests
 
diff --git a/sql/item.h b/sql/item.h
index 139ce40b25b..dcd773ffc59 100644
--- a/sql/item.h
+++ b/sql/item.h
@@ -1449,6 +1449,11 @@ public:
   virtual bool exists2in_processor(uchar *opt_arg) { return 0; }
   virtual bool find_selective_predicates_list_processor(uchar *opt_arg)
   { return 0; }
+  bool cleanup_is_expensive_cache_processor(uchar *arg)
+  {
+    is_expensive_cache= (int8)(-1);
+    return 0;
+  }
 
   /* To call bool function for all arguments */
   struct bool_func_call_args
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index e3b725ce1f6..460a64e1a7a 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -1212,6 +1212,13 @@ JOIN::optimize_inner()
   if (optimize_constant_subqueries())
     DBUG_RETURN(1);
 
+  if (conds && conds->has_subquery())
+    (void) conds->walk(&Item::cleanup_is_expensive_cache_processor,
+                       0, (uchar*)0);
+  if (having && having->has_subquery())
+    (void) having->walk(&Item::cleanup_is_expensive_cache_processor,
+                       0, (uchar*)0);
+
   if (setup_jtbm_semi_joins(this, join_list, &conds))
     DBUG_RETURN(1);