MDEV-38240: Selectivity sampling not performed when the table has no indexed conditions

Don't skip range analysis step in such cases.

Author: spetrunia

mysql-test/main/selectivity.result

@@ -2114,4 +2114,32 @@ a	b	c	d	e
 2	NULL	NULL	NULL	NULL
 set join_cache_level= default;
 DROP TABLE t1, t2, t3;
+#
+# MDEV-38240: Selectivity sampling not performed when the table has no indexed conditions
+#
+set use_stat_tables=PREFERABLY;
+create table t1 (a varchar(100), b int);
+insert into t1 select seq, seq from seq_1_to_1000;
+analyze table t1;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	Engine-independent statistics collected
+test.t1	analyze	status	OK
+set optimizer_use_condition_selectivity=5;
+# Must produce filtered=1% or so:
+explain extended
+select * from t1 where a like '%99%';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	1000	1.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b` from `test`.`t1` where `test`.`t1`.`a` like '%99%'
+# Must have same filtered as above
+explain extended
+select * from t1 where a like '%99%' and (b is null or b is not null);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	1000	1.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b` from `test`.`t1` where `test`.`t1`.`a` like '%99%' and (`test`.`t1`.`b` is null or `test`.`t1`.`b` is not null)
+drop table t1;
+set optimizer_use_condition_selectivity= @save_optimizer_use_condition_selectivity;
+set use_stat_tables= @save_use_stat_tables;
 ALTER DATABASE test CHARACTER SET utf8mb4 COLLATE utf8mb4_uca1400_ai_ci;

mysql-test/main/selectivity.test

@@ -1456,4 +1456,25 @@ SELECT * FROM t1 LEFT JOIN (t2 JOIN t3 ON t2.b = t3.e) ON t2.c = 1;
 set join_cache_level= default;
 DROP TABLE t1, t2, t3;
 
+--echo #
+--echo # MDEV-38240: Selectivity sampling not performed when the table has no indexed conditions
+--echo #
+set use_stat_tables=PREFERABLY;
+create table t1 (a varchar(100), b int);
+insert into t1 select seq, seq from seq_1_to_1000;
+analyze table t1;
+
+set optimizer_use_condition_selectivity=5;
+--echo # Must produce filtered=1% or so:
+explain extended
+select * from t1 where a like '%99%';
+
+--echo # Must have same filtered as above
+explain extended
+select * from t1 where a like '%99%' and (b is null or b is not null);
+drop table t1;
+
+set optimizer_use_condition_selectivity= @save_optimizer_use_condition_selectivity;
+set use_stat_tables= @save_use_stat_tables;
+
 --source include/test_db_charset_restore.inc

mysql-test/main/selectivity_innodb.result

@@ -2121,6 +2121,34 @@ a	b	c	d	e
 2	NULL	NULL	NULL	NULL
 set join_cache_level= default;
 DROP TABLE t1, t2, t3;
+#
+# MDEV-38240: Selectivity sampling not performed when the table has no indexed conditions
+#
+set use_stat_tables=PREFERABLY;
+create table t1 (a varchar(100), b int);
+insert into t1 select seq, seq from seq_1_to_1000;
+analyze table t1;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	Engine-independent statistics collected
+test.t1	analyze	status	OK
+set optimizer_use_condition_selectivity=5;
+# Must produce filtered=1% or so:
+explain extended
+select * from t1 where a like '%99%';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	1000	1.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b` from `test`.`t1` where `test`.`t1`.`a` like '%99%'
+# Must have same filtered as above
+explain extended
+select * from t1 where a like '%99%' and (b is null or b is not null);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	1000	1.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b` from `test`.`t1` where `test`.`t1`.`a` like '%99%' and (`test`.`t1`.`b` is null or `test`.`t1`.`b` is not null)
+drop table t1;
+set optimizer_use_condition_selectivity= @save_optimizer_use_condition_selectivity;
+set use_stat_tables= @save_use_stat_tables;
 ALTER DATABASE test CHARACTER SET utf8mb4 COLLATE utf8mb4_uca1400_ai_ci;
 set optimizer_switch=@save_optimizer_switch_for_selectivity_test;
 set @tmp_ust= @@use_stat_tables;

sql/sql_select.cc

@@ -6220,15 +6220,21 @@ make_join_statistics(JOIN *join, List<TABLE_LIST> &tables_list,
                   s->table->opt_range_condition_rows /
                   s->table->used_stat_records);
       /*
-        Perform range analysis if there are keys it could use (1).
-        Don't do range analysis for materialized subqueries (2).
-        Don't do range analysis for materialized derived tables/views (3)
+        Perform range analysis if we could infer something from it.
+        (1) There are indexes for which we have range conditions,
+        (2) Or there are sargable conditions on the table's columns that we
+            could use for selectivity estimation,
+        (3) Or selectivity estimation via sampling is enabled.
+
+        (4) Don't do range analysis for materialized subqueries.
+        (5) Don't do range analysis for materialized derived tables/views.
       */
-      if ((!s->const_keys.is_clear_all() ||
-           !bitmap_is_clear_all(&s->table->cond_set)) &&              // (1)
-          !s->table->is_filled_at_execution() &&                      // (2)
-          !(s->table->pos_in_table_list->derived &&                   // (3)
-            s->table->pos_in_table_list->is_materialized_derived()))  // (3)
+      if ((!s->const_keys.is_clear_all() ||                            // (1)
+           !bitmap_is_clear_all(&s->table->cond_set) ||                // (2)
+           thd->variables.optimizer_use_condition_selectivity >= 5) && // (3)
+          !s->table->is_filled_at_execution() &&                       // (4)
+          !(s->table->pos_in_table_list->derived &&                    // (5)
+            s->table->pos_in_table_list->is_materialized_derived()))   // (5)
       {
         bool impossible_range= FALSE;
         ha_rows records= HA_ROWS_MAX;