MDEV-30081 Crash with splitting from constant mergeable derived table

This bug manifested itself in very rare situations when splitting
optimization was applied to a materialized derived table with group clause
by key over a constant meargeable derived table that was in inner part of
an outer join. In this case the used tables for the key to access the
split table incorrectly was evaluated to a not empty table map.

Approved by Oleksandr Byelkin <sanja@mariadb.com>

mysql-test/main/derived_cond_pushdown.result

@@ -18131,4 +18131,62 @@ DROP TABLE transaction_items;
 DROP TABLE transactions;
 DROP TABLE charges;
 DROP TABLE ledgers;
+#
+# MDEV-30081: Splitting from a constant mergeable derived table
+#             used in inner part of an outer join.
+#
+CREATE TABLE t1 ( id int PRIMARY KEY ) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (3),(4),(7);
+CREATE TABLE t2 (
+id int,  id1 int, wid int, PRIMARY KEY (id), KEY (id1), KEY (wid)
+) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (4,4,6),(7,7,7);
+CREATE TABLE t3 (
+wid int, wtid int, otid int, oid int,
+PRIMARY KEY (wid), KEY (wtid), KEY (otid), KEY (oid)
+) ENGINE=MyISAM;
+INSERT INTO t3 VALUES (6,30,6,6),(7,17,7,7);
+CREATE TABLE t4 ( id int, a int, PRIMARY KEY (id), KEY (a) )  ENGINE=MyISAM;
+INSERT INTO t4 VALUES (1,17),(2,15),(3,49),(4,3),(5,45),(6,38),(7,17);
+CREATE TABLE t5 (
+id int, id1 int, PRIMARY KEY (id), KEY id1 (id1)
+) ENGINE=MyISAM ;
+INSERT INTO t5 VALUES (1,17),(2,15),(3,49),(4,3),(5,45),(6,38),(7,17);
+ANALYZE TABLE t1,t2,t3,t4,t5;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	OK
+test.t2	analyze	status	OK
+test.t3	analyze	status	OK
+test.t4	analyze	status	OK
+test.t5	analyze	status	OK
+CREATE VIEW v1 AS (SELECT id1 FROM t5 GROUP BY id1);
+SELECT t3.*, t1.id AS t1_id, t2.id AS t2_id, dt.*, v1.*
+FROM
+t1, t2, t3
+LEFT JOIN
+(SELECT t4.* FROM t4 WHERE t4.a=3) dt
+ON t3.oid = dt.id AND t3.otid = 14
+LEFT JOIN v1
+ON (v1.id1 = dt.a)
+WHERE t3.oid = t1.id AND t3.oid = t2.id AND t3.wid = 7;
+wid	wtid	otid	oid	t1_id	t2_id	id	a	id1
+7	17	7	7	7	7	NULL	NULL	NULL
+EXPLAIN SELECT t3.*, t1.id AS t1_id, t2.id AS t2_id, dt.*, v1.*
+FROM
+t1, t2, t3
+LEFT JOIN
+(SELECT t4.* FROM t4 WHERE t4.a=3) dt
+ON t3.oid = dt.id AND t3.otid = 14
+LEFT JOIN v1
+ON (v1.id1 = dt.a)
+WHERE t3.oid = t1.id AND t3.oid = t2.id AND t3.wid = 7;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t3	const	PRIMARY,oid	PRIMARY	4	const	1	
+1	PRIMARY	t1	const	PRIMARY	PRIMARY	4	const	1	Using index
+1	PRIMARY	t2	const	PRIMARY	PRIMARY	4	const	1	Using index
+1	PRIMARY	t4	const	PRIMARY,a	NULL	NULL	NULL	1	Impossible ON condition
+1	PRIMARY	<derived3>	ref	key0	key0	5	const	0	Using where
+3	LATERAL DERIVED	t5	ref	id1	id1	5	const	0	Using index
+DROP VIEW v1;
+DROP TABLE t1,t2,t3,t4,t5;
 # End of 10.3 tests

mysql-test/main/derived_cond_pushdown.test

@@ -3853,4 +3853,53 @@ DROP TABLE transactions;
 DROP TABLE charges;
 DROP TABLE ledgers;
 
+
+--echo #
+--echo # MDEV-30081: Splitting from a constant mergeable derived table
+--echo #             used in inner part of an outer join.
+--echo #
+
+  CREATE TABLE t1 ( id int PRIMARY KEY ) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (3),(4),(7);
+
+CREATE TABLE t2 (
+  id int,  id1 int, wid int, PRIMARY KEY (id), KEY (id1), KEY (wid)
+) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (4,4,6),(7,7,7);
+
+CREATE TABLE t3 (
+  wid int, wtid int, otid int, oid int,
+  PRIMARY KEY (wid), KEY (wtid), KEY (otid), KEY (oid)
+) ENGINE=MyISAM;
+INSERT INTO t3 VALUES (6,30,6,6),(7,17,7,7);
+
+CREATE TABLE t4 ( id int, a int, PRIMARY KEY (id), KEY (a) )  ENGINE=MyISAM;
+INSERT INTO t4 VALUES (1,17),(2,15),(3,49),(4,3),(5,45),(6,38),(7,17);
+
+CREATE TABLE t5 (
+  id int, id1 int, PRIMARY KEY (id), KEY id1 (id1)
+) ENGINE=MyISAM ;
+INSERT INTO t5 VALUES (1,17),(2,15),(3,49),(4,3),(5,45),(6,38),(7,17);
+
+ANALYZE TABLE t1,t2,t3,t4,t5;
+
+CREATE VIEW v1 AS (SELECT id1 FROM t5 GROUP BY id1);
+
+let $q=
+SELECT t3.*, t1.id AS t1_id, t2.id AS t2_id, dt.*, v1.*
+FROM
+  t1, t2, t3
+  LEFT JOIN
+  (SELECT t4.* FROM t4 WHERE t4.a=3) dt
+  ON t3.oid = dt.id AND t3.otid = 14
+  LEFT JOIN v1
+  ON (v1.id1 = dt.a)
+WHERE t3.oid = t1.id AND t3.oid = t2.id AND t3.wid = 7;
+
+eval $q;
+eval EXPLAIN $q;
+
+DROP VIEW v1;
+DROP TABLE t1,t2,t3,t4,t5;
+
 --echo # End of 10.3 tests

sql/item.cc

@@ -10838,7 +10838,7 @@ table_map Item_direct_view_ref::used_tables() const
     table_map used= (*ref)->used_tables();
     return (used ?
             used :
-            ((null_ref_table != NO_NULL_TABLE) ?
+            (null_ref_table != NO_NULL_TABLE && !null_ref_table->const_table ?
              null_ref_table->map :
              (table_map)0 ));
   }