From f4484dfdbf2d78b0f357916ebd8ade024dd73c09 Mon Sep 17 00:00:00 2001
From: Alexander Barkov <bar@mariadb.com>
Date: Thu, 21 Mar 2019 13:43:17 +0400
Subject: [PATCH] MDEV-19008 Slow EXPLAIN SELECT ... WHERE col IN
 (const1,const2,(subquery))

---
 mysql-test/main/func_debug.result | 19 +++++++++++++++++++
 mysql-test/main/func_debug.test   | 13 +++++++++++++
 sql/item.h                        | 10 ++++++++++
 sql/item_cmpfunc.h                |  2 +-
 sql/item_subselect.cc             |  6 ++++++
 5 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/mysql-test/main/func_debug.result b/mysql-test/main/func_debug.result
index 7fcf522abba2a..e2bf0ca8df341 100644
--- a/mysql-test/main/func_debug.result
+++ b/mysql-test/main/func_debug.result
@@ -1655,3 +1655,22 @@ Note	1105	DBUG: [1] arg=2 handler=0 (time)
 Note	1105	DBUG: [2] arg=3 handler=2 (datetime)
 SET SESSION debug_dbug="-d,Predicant_to_list_comparator";
 SET SESSION debug_dbug="-d,Item_func_in";
+#
+# MDEV-19008 Slow EXPLAIN SELECT ... WHERE col IN (const1,const2,(subquery))
+#
+SET SESSION debug_dbug="+d,Item_subselect";
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+EXPLAIN SELECT * FROM t1 WHERE a IN (1,2,(SELECT MAX(a) FROM t1));
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	10	Using where
+2	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	10	
+SELECT * FROM t1 WHERE a IN (1,2,(SELECT MAX(a) FROM t1));
+a
+1
+2
+9
+Warnings:
+Note	1105	DBUG: Item_subselect::exec (select max(`test`.`t1`.`a`) from `test`.`t1`)
+DROP TABLE t1;
+SET SESSION debug_dbug="-d,Item_subselect";
diff --git a/mysql-test/main/func_debug.test b/mysql-test/main/func_debug.test
index e0960f736cb54..8dd01650ed36b 100644
--- a/mysql-test/main/func_debug.test
+++ b/mysql-test/main/func_debug.test
@@ -475,3 +475,16 @@ SELECT
 
 SET SESSION debug_dbug="-d,Predicant_to_list_comparator";
 SET SESSION debug_dbug="-d,Item_func_in";
+
+
+--echo #
+--echo # MDEV-19008 Slow EXPLAIN SELECT ... WHERE col IN (const1,const2,(subquery))
+--echo #
+
+SET SESSION debug_dbug="+d,Item_subselect";
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+EXPLAIN SELECT * FROM t1 WHERE a IN (1,2,(SELECT MAX(a) FROM t1));
+SELECT * FROM t1 WHERE a IN (1,2,(SELECT MAX(a) FROM t1));
+DROP TABLE t1;
+SET SESSION debug_dbug="-d,Item_subselect";
diff --git a/sql/item.h b/sql/item.h
index 4eab7090276d4..883cc791f3843 100644
--- a/sql/item.h
+++ b/sql/item.h
@@ -1409,6 +1409,16 @@ class Item: public Value_source,
                      LOWEST_PRECEDENCE);
   }
   virtual void print(String *str, enum_query_type query_type);
+
+  class Print: public String
+  {
+  public:
+    Print(Item *item, enum_query_type type)
+    {
+      item->print(this, type);
+    }
+  };
+
   void print_item_w_name(String *str, enum_query_type query_type);
   void print_value(String *str);
 
diff --git a/sql/item_cmpfunc.h b/sql/item_cmpfunc.h
index 4a1202837f49f..06f15503258a3 100644
--- a/sql/item_cmpfunc.h
+++ b/sql/item_cmpfunc.h
@@ -2281,7 +2281,7 @@ class Item_func_in :public Item_func_opt_neg,
   {
     for (uint i= 0; i < nitems; i++)
     {
-      if (!items[i]->const_item())
+      if (!items[i]->const_item() || items[i]->is_expensive())
         return false;
     }
     return true;
diff --git a/sql/item_subselect.cc b/sql/item_subselect.cc
index 207aa9a25c98a..cd411c5d4c110 100644
--- a/sql/item_subselect.cc
+++ b/sql/item_subselect.cc
@@ -710,6 +710,12 @@ bool Item_subselect::exec()
   DBUG_ENTER("Item_subselect::exec");
   DBUG_ASSERT(fixed);
 
+  DBUG_EXECUTE_IF("Item_subselect",
+                  push_warning_printf(thd, Sql_condition::WARN_LEVEL_NOTE,
+                  ER_UNKNOWN_ERROR, "DBUG: Item_subselect::exec %s",
+                  Item::Print(this,
+                              enum_query_type(QT_TO_SYSTEM_CHARSET |
+                                              QT_WITHOUT_INTRODUCERS)).ptr()););
   /*
     Do not execute subselect in case of a fatal error
     or if the query has been killed.