MDEV-20424: New default value for optimizer_use_condition-selectivity leads to bad plan

In the function prev_record_reads where one finds the different row combinations for a
subset of partial join, it did not take into account the selectivity of tables
involved in the subset of partial join.

mysql-test/r/selectivity.result

@@ -1753,4 +1753,61 @@ a
 1991
 set optimizer_use_condition_selectivity=@save_optimizer_use_condition_selectivity;
 DROP TABLE t1;
+#
+# MDEV-20424: New default value for optimizer_use_condition-selectivity
+# leads to bad plan
+#
+create table t1(a int, b int, c int, d int, key(a,b));
+insert into t1 select 50,seq-1,seq-1,seq from seq_1_to_10;
+insert into t1 select seq-1,seq-1,seq-1,seq from seq_1_to_100 limit 90;
+create table t2(a int, b int, c int, primary key(a));
+insert into t2 select seq-1,seq-1,seq-1 from seq_1_to_100;
+create table t3(a int, b int, c int, primary key(a));
+insert into t3 select seq-1,seq-1,seq-1 from seq_1_to_100 limit 30;
+set optimizer_use_condition_selectivity=1;
+explain extended select t1.b,t2.a,t3.a,t3.b from t1,t2,t3
+where t1.c = t2.a AND t1.d = t3.a and t1.a = 50 and t1.b <= 100;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	range	a	a	10	NULL	9	100.00	Using index condition; Using where
+1	SIMPLE	t3	eq_ref	PRIMARY	PRIMARY	4	test.t1.d	1	100.00	
+1	SIMPLE	t2	eq_ref	PRIMARY	PRIMARY	4	test.t1.c	1	100.00	Using index
+Warnings:
+Note	1003	select `test`.`t1`.`b` AS `b`,`test`.`t2`.`a` AS `a`,`test`.`t3`.`a` AS `a`,`test`.`t3`.`b` AS `b` from `test`.`t1` join `test`.`t2` join `test`.`t3` where ((`test`.`t2`.`a` = `test`.`t1`.`c`) and (`test`.`t3`.`a` = `test`.`t1`.`d`) and (`test`.`t1`.`a` = 50) and (`test`.`t1`.`b` <= 100))
+select t1.b,t2.a,t3.a,t3.b from t1,t2,t3
+where t1.c = t2.a AND t1.d = t3.a and t1.a = 50 and t1.b <= 100;
+b	a	a	b
+0	0	1	1
+1	1	2	2
+2	2	3	3
+3	3	4	4
+4	4	5	5
+5	5	6	6
+6	6	7	7
+7	7	8	8
+8	8	9	9
+9	9	10	10
+set optimizer_use_condition_selectivity=2;
+explain extended select t1.b,t2.a,t3.a,t3.b from t1,t2,t3
+where t1.c = t2.a AND t1.d = t3.a and t1.a = 50 and t1.b <= 100;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	range	a	a	10	NULL	9	9.00	Using index condition; Using where
+1	SIMPLE	t3	eq_ref	PRIMARY	PRIMARY	4	test.t1.d	1	100.00	
+1	SIMPLE	t2	eq_ref	PRIMARY	PRIMARY	4	test.t1.c	1	100.00	Using index
+Warnings:
+Note	1003	select `test`.`t1`.`b` AS `b`,`test`.`t2`.`a` AS `a`,`test`.`t3`.`a` AS `a`,`test`.`t3`.`b` AS `b` from `test`.`t1` join `test`.`t2` join `test`.`t3` where ((`test`.`t2`.`a` = `test`.`t1`.`c`) and (`test`.`t3`.`a` = `test`.`t1`.`d`) and (`test`.`t1`.`a` = 50) and (`test`.`t1`.`b` <= 100))
+select t1.b,t2.a,t3.a,t3.b from t1,t2,t3
+where t1.c = t2.a AND t1.d = t3.a and t1.a = 50 and t1.b <= 100;
+b	a	a	b
+0	0	1	1
+1	1	2	2
+2	2	3	3
+3	3	4	4
+4	4	5	5
+5	5	6	6
+6	6	7	7
+7	7	8	8
+8	8	9	9
+9	9	10	10
+set optimizer_use_condition_selectivity= @@optimizer_use_condition_selectivity;
+drop table t1,t2,t3;
 # End of 10.1 tests

mysql-test/r/selectivity_innodb.result

@@ -1763,6 +1763,63 @@ a
 1991
 set optimizer_use_condition_selectivity=@save_optimizer_use_condition_selectivity;
 DROP TABLE t1;
+#
+# MDEV-20424: New default value for optimizer_use_condition-selectivity
+# leads to bad plan
+#
+create table t1(a int, b int, c int, d int, key(a,b));
+insert into t1 select 50,seq-1,seq-1,seq from seq_1_to_10;
+insert into t1 select seq-1,seq-1,seq-1,seq from seq_1_to_100 limit 90;
+create table t2(a int, b int, c int, primary key(a));
+insert into t2 select seq-1,seq-1,seq-1 from seq_1_to_100;
+create table t3(a int, b int, c int, primary key(a));
+insert into t3 select seq-1,seq-1,seq-1 from seq_1_to_100 limit 30;
+set optimizer_use_condition_selectivity=1;
+explain extended select t1.b,t2.a,t3.a,t3.b from t1,t2,t3
+where t1.c = t2.a AND t1.d = t3.a and t1.a = 50 and t1.b <= 100;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	range	a	a	10	NULL	11	100.00	Using index condition; Using where
+1	SIMPLE	t3	eq_ref	PRIMARY	PRIMARY	4	test.t1.d	1	100.00	
+1	SIMPLE	t2	eq_ref	PRIMARY	PRIMARY	4	test.t1.c	1	100.00	Using index
+Warnings:
+Note	1003	select `test`.`t1`.`b` AS `b`,`test`.`t2`.`a` AS `a`,`test`.`t3`.`a` AS `a`,`test`.`t3`.`b` AS `b` from `test`.`t1` join `test`.`t2` join `test`.`t3` where ((`test`.`t2`.`a` = `test`.`t1`.`c`) and (`test`.`t3`.`a` = `test`.`t1`.`d`) and (`test`.`t1`.`a` = 50) and (`test`.`t1`.`b` <= 100))
+select t1.b,t2.a,t3.a,t3.b from t1,t2,t3
+where t1.c = t2.a AND t1.d = t3.a and t1.a = 50 and t1.b <= 100;
+b	a	a	b
+0	0	1	1
+1	1	2	2
+2	2	3	3
+3	3	4	4
+4	4	5	5
+5	5	6	6
+6	6	7	7
+7	7	8	8
+8	8	9	9
+9	9	10	10
+set optimizer_use_condition_selectivity=2;
+explain extended select t1.b,t2.a,t3.a,t3.b from t1,t2,t3
+where t1.c = t2.a AND t1.d = t3.a and t1.a = 50 and t1.b <= 100;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	range	a	a	10	NULL	11	11.00	Using index condition; Using where
+1	SIMPLE	t3	eq_ref	PRIMARY	PRIMARY	4	test.t1.d	1	100.00	
+1	SIMPLE	t2	eq_ref	PRIMARY	PRIMARY	4	test.t1.c	1	100.00	Using index
+Warnings:
+Note	1003	select `test`.`t1`.`b` AS `b`,`test`.`t2`.`a` AS `a`,`test`.`t3`.`a` AS `a`,`test`.`t3`.`b` AS `b` from `test`.`t1` join `test`.`t2` join `test`.`t3` where ((`test`.`t2`.`a` = `test`.`t1`.`c`) and (`test`.`t3`.`a` = `test`.`t1`.`d`) and (`test`.`t1`.`a` = 50) and (`test`.`t1`.`b` <= 100))
+select t1.b,t2.a,t3.a,t3.b from t1,t2,t3
+where t1.c = t2.a AND t1.d = t3.a and t1.a = 50 and t1.b <= 100;
+b	a	a	b
+0	0	1	1
+1	1	2	2
+2	2	3	3
+3	3	4	4
+4	4	5	5
+5	5	6	6
+6	6	7	7
+7	7	8	8
+8	8	9	9
+9	9	10	10
+set optimizer_use_condition_selectivity= @@optimizer_use_condition_selectivity;
+drop table t1,t2,t3;
 # End of 10.1 tests
 set optimizer_switch=@save_optimizer_switch_for_selectivity_test;
 set @tmp_ust= @@use_stat_tables;

mysql-test/t/selectivity.test

@@ -1205,5 +1205,34 @@ set optimizer_use_condition_selectivity=@save_optimizer_use_condition_selectivit
 
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-20424: New default value for optimizer_use_condition-selectivity
+--echo # leads to bad plan
+--echo #
+
+create table t1(a int, b int, c int, d int, key(a,b));
+insert into t1 select 50,seq-1,seq-1,seq from seq_1_to_10;
+insert into t1 select seq-1,seq-1,seq-1,seq from seq_1_to_100 limit 90;
+
+create table t2(a int, b int, c int, primary key(a));
+insert into t2 select seq-1,seq-1,seq-1 from seq_1_to_100;
+
+create table t3(a int, b int, c int, primary key(a));
+insert into t3 select seq-1,seq-1,seq-1 from seq_1_to_100 limit 30;
+
+let $query= select t1.b,t2.a,t3.a,t3.b from t1,t2,t3
+where t1.c = t2.a AND t1.d = t3.a and t1.a = 50 and t1.b <= 100;
+
+set optimizer_use_condition_selectivity=1;
+eval explain extended $query;
+eval $query;
+
+set optimizer_use_condition_selectivity=2;
+eval explain extended $query;
+eval $query;
+set optimizer_use_condition_selectivity= @@optimizer_use_condition_selectivity;
+
+drop table t1,t2,t3;
+
 --echo # End of 10.1 tests
 

sql/sql_select.cc

@@ -8470,7 +8470,10 @@ prev_record_reads(POSITION *positions, uint idx, table_map found_ref)
           #max_nested_outer_joins=64-1) will not make it any more precise.
       */
       if (pos->records_read)
+      {
         found= COST_MULT(found, pos->records_read);
+        found*= pos->cond_selectivity;
+      }
      }
   }
   return found;