MDEV-17039: Query plan changes when we use GROUP BY optimization with...

MDEV-17039: Query plan changes when we use GROUP BY optimization with optimizer_use_condition_selectivity=4
            and use_stat_tables= PREFERABLY

Currently the code that calculates selectivity for a table does not take into account the case when
we can have GROUP BY optimization (looses index scan).

mysql-test/r/group_min_max.result

@@ -3733,5 +3733,33 @@ id	MIN(a)	MAX(a)
 4	 2001-01-04	 2001-01-04
 DROP TABLE t1;
 #
+# Query plan changes when we use GROUP BY optimization with optimizer_use_condition_selectivity=4
+# and use_stat_tables= PREFERABLY
+#
+CREATE TABLE t1 (a INT, b INT,c INT DEFAULT 0, INDEX (a,b));
+INSERT INTO t1 (a, b) VALUES (1,1), (1,2), (1,3), (1,4), (1,5),
+(2,2), (2,3), (2,1), (3,1), (4,1), (4,2), (4,3), (4,4), (4,5), (4,6);
+set @save_optimizer_use_condition_selectivity= @@optimizer_use_condition_selectivity;
+set @save_use_stat_tables= @@use_stat_tables;
+set @@optimizer_use_condition_selectivity=4;
+set @@use_stat_tables=PREFERABLY;
+explain extended SELECT a FROM t1 AS t1_outer WHERE a IN (SELECT max(b) FROM t1  GROUP BY a);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	<subquery2>	ALL	distinct_key	NULL	NULL	NULL	8	100.00	
+1	PRIMARY	t1_outer	ref	a	a	5	<subquery2>.max(b)	2	100.00	Using index
+2	MATERIALIZED	t1	range	NULL	a	5	NULL	8	100.00	Using index for group-by
+Warnings:
+Note	1003	select `test`.`t1_outer`.`a` AS `a` from  <materialize> (select max(`test`.`t1`.`b`) from `test`.`t1` group by `test`.`t1`.`a`) join `test`.`t1` `t1_outer` where (`test`.`t1_outer`.`a` = `<subquery2>`.`max(b)`)
+set @@optimizer_use_condition_selectivity=@save_optimizer_use_condition_selectivity;
+set @@use_stat_tables=@save_use_stat_tables;
+explain extended SELECT a FROM t1 AS t1_outer WHERE a IN (SELECT max(b) FROM t1   GROUP BY a);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	PRIMARY	<subquery2>	ALL	distinct_key	NULL	NULL	NULL	8	100.00	
+1	PRIMARY	t1_outer	ref	a	a	5	<subquery2>.max(b)	2	100.00	Using index
+2	MATERIALIZED	t1	range	NULL	a	5	NULL	8	100.00	Using index for group-by
+Warnings:
+Note	1003	select `test`.`t1_outer`.`a` AS `a` from  <materialize> (select max(`test`.`t1`.`b`) from `test`.`t1` group by `test`.`t1`.`a`) join `test`.`t1` `t1_outer` where (`test`.`t1_outer`.`a` = `<subquery2>`.`max(b)`)
+drop table t1;
+#
 # End of 10.0 tests
 #

mysql-test/t/group_min_max.test

@@ -1519,6 +1519,23 @@ ALTER TABLE t1 ADD KEY(id,a);
 SELECT id,MIN(a),MAX(a) FROM t1 WHERE a>=DATE'2001-01-04' GROUP BY id;
 DROP TABLE t1;
 
+--echo #
+--echo # Query plan changes when we use GROUP BY optimization with optimizer_use_condition_selectivity=4
+--echo # and use_stat_tables= PREFERABLY
+--echo #
+
+CREATE TABLE t1 (a INT, b INT,c INT DEFAULT 0, INDEX (a,b));
+INSERT INTO t1 (a, b) VALUES (1,1), (1,2), (1,3), (1,4), (1,5),
+(2,2), (2,3), (2,1), (3,1), (4,1), (4,2), (4,3), (4,4), (4,5), (4,6);
+set @save_optimizer_use_condition_selectivity= @@optimizer_use_condition_selectivity;
+set @save_use_stat_tables= @@use_stat_tables;
+set @@optimizer_use_condition_selectivity=4;
+set @@use_stat_tables=PREFERABLY;
+explain extended SELECT a FROM t1 AS t1_outer WHERE a IN (SELECT max(b) FROM t1  GROUP BY a); 
+set @@optimizer_use_condition_selectivity=@save_optimizer_use_condition_selectivity;
+set @@use_stat_tables=@save_use_stat_tables;
+explain extended SELECT a FROM t1 AS t1_outer WHERE a IN (SELECT max(b) FROM t1   GROUP BY a); 
+drop table t1; 
 
 --echo #
 --echo # End of 10.0 tests

sql/opt_range.cc

@@ -3501,7 +3501,18 @@ bool calculate_cond_selectivity_for_table(THD *thd, TABLE *table, Item *cond)
 
   table->cond_selectivity= 1.0;
 
-  if (!cond || table_records == 0)
+  if (table_records == 0)
+    DBUG_RETURN(FALSE);
+
+  QUICK_SELECT_I *quick;
+  if ((quick=table->reginfo.join_tab->quick) &&
+      quick->get_type() == QUICK_SELECT_I::QS_TYPE_GROUP_MIN_MAX)
+  {
+    table->cond_selectivity*= (quick->records/table_records);
+    DBUG_RETURN(FALSE);
+  }
+
+  if (!cond)
     DBUG_RETURN(FALSE);
 
   if (table->pos_in_table_list->schema_table)