MDEV-3900 Optimizer difference between MySQL and MariaDB with stored functions...

MDEV-3900 Optimizer difference between MySQL and MariaDB with stored functions in WHERE clause of UPDATE or DELETE statements

Analysis
The reason for the less efficient plan was result of a prior design decision -
to limit the eveluation of constant expressions during optimization to only
non-expensive ones. With this approach all stored procedures were considered
expensive, and were not evaluated during optimization. As a result, SPs didn't
participate in range optimization, which resulted in a plan with table scan
rather than index range scan.

Solution
Instead of considering all SPs expensive, consider expensive only those SPs
that are non-deterministic. If an SP is deterministic, the optimizer will
checj if it is constant, and may eventually evaluate it during optimization.

mysql-test/r/sp.result

@@ -6420,16 +6420,16 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ref	c1	c1	5	const	1	Using index
 EXPLAIN SELECT * FROM t1 WHERE c1=f1();
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	ref	c1	c1	5	const	0	Using index
+1	SIMPLE	t1	ref	c1	c1	5	const	1	Using index
 EXPLAIN SELECT * FROM v1 WHERE c1=1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ref	c1	c1	5	const	1	Using index
 EXPLAIN SELECT * FROM v1 WHERE c1=f1();
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	ref	c1	c1	5	const	0	Using index
+1	SIMPLE	t1	ref	c1	c1	5	const	1	Using index
 EXPLAIN SELECT * FROM t1 WHERE c1=f2(10);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	ref	c1	c1	5	const	0	Using index
+1	SIMPLE	t1	ref	c1	c1	5	const	1	Using index
 EXPLAIN SELECT * FROM t1 WHERE c1=f2(c1);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	index	NULL	c1	5	NULL	5	Using where; Using index
@@ -7146,3 +7146,33 @@ c1	c2	count(c3)
 2012-03-01 01:00:00	3	1
 2012-03-01 02:00:00	3	1
 DROP PROCEDURE p1;
+
+MDEV-3900 Optimizer difference between MySQL and MariaDB with stored functions in WHERE clause of UPDATE or DELETE statements
+
+CREATE FUNCTION tdn() RETURNS int(7) DETERMINISTIC RETURN to_days(now());
+CREATE TABLE t1 (pk INT NOT NULL AUTO_INCREMENT PRIMARY KEY, daynum INT, a CHAR(1), INDEX(daynum), INDEX(a)) ENGINE=MyISAM;
+INSERT INTO t1 (daynum) VALUES (1),(2),(3),(4),(5),(TO_DAYS(NOW())),(7),(8);
+INSERT INTO t1 (daynum) SELECT a1.daynum FROM t1 a1, t1 a2, t1 a3, t1 a4, t1 a5;
+FLUSH TABLES;
+FLUSH STATUS;
+SHOW STATUS LIKE '%Handler_read%';
+Variable_name	Value
+Handler_read_first	0
+Handler_read_key	0
+Handler_read_next	0
+Handler_read_prev	0
+Handler_read_rnd	0
+Handler_read_rnd_deleted	0
+Handler_read_rnd_next	0
+UPDATE t1 SET a = '+' WHERE daynum=tdn();
+SHOW STATUS LIKE '%Handler_read%';
+Variable_name	Value
+Handler_read_first	0
+Handler_read_key	2
+Handler_read_next	4097
+Handler_read_prev	0
+Handler_read_rnd	0
+Handler_read_rnd_deleted	0
+Handler_read_rnd_next	0
+drop function tdn;
+drop table t1;

mysql-test/t/sp.test

@@ -8478,3 +8478,22 @@ CALL p1(1);
 
 DROP PROCEDURE p1;
 
+--echo
+--echo MDEV-3900 Optimizer difference between MySQL and MariaDB with stored functions in WHERE clause of UPDATE or DELETE statements
+--echo
+
+CREATE FUNCTION tdn() RETURNS int(7) DETERMINISTIC RETURN to_days(now());
+
+CREATE TABLE t1 (pk INT NOT NULL AUTO_INCREMENT PRIMARY KEY, daynum INT, a CHAR(1), INDEX(daynum), INDEX(a)) ENGINE=MyISAM;
+INSERT INTO t1 (daynum) VALUES (1),(2),(3),(4),(5),(TO_DAYS(NOW())),(7),(8);
+INSERT INTO t1 (daynum) SELECT a1.daynum FROM t1 a1, t1 a2, t1 a3, t1 a4, t1 a5;
+
+FLUSH TABLES;
+FLUSH STATUS;
+
+SHOW STATUS LIKE '%Handler_read%';
+UPDATE t1 SET a = '+' WHERE daynum=tdn();
+SHOW STATUS LIKE '%Handler_read%';
+
+drop function tdn;
+drop table t1;

sql/item_func.cc

@@ -6056,6 +6056,19 @@ Item_func_sp::init_result_field(THD *thd)
 }
 
 
+/**
+  @note
+  Deterministic stored procedures are considered inexpensive.
+  Consequently such procedures may be evaluated during optimization,
+  if they are constant (checked by the optimizer).
+*/
+
+bool Item_func_sp::is_expensive()
+{
+  return !(m_sp->m_chistics->detistic);
+}
+
+
 /**
   @brief Initialize local members with values from the Field interface.
 

sql/item_func.h

@@ -1807,7 +1807,8 @@ class Item_func_sp :public Item_func
   bool init_result_field(THD *thd);
 
 protected:
-  bool is_expensive_processor(uchar *arg) { return TRUE; }
+  bool is_expensive_processor(uchar *arg)
+  { return is_expensive(); }
   
 public:
 
@@ -1881,7 +1882,7 @@ class Item_func_sp :public Item_func
 
   bool fix_fields(THD *thd, Item **ref);
   void fix_length_and_dec(void);
-  bool is_expensive() { return 1; }
+  bool is_expensive();
 
   inline Field *get_sp_result_field()
   {