MDEV-4465: Reproducible crash (mysqld got signal 11) in multi_delete::initialize_tables...

- make multi_delete::initialize_tables() take into account that the JOIN structure may have
  semi-join nests (which are not fully initialized when this function is called, they have 
  tab->table=NULL which caused the crash)
- Also checked multi_update::initialize_tables(): it has a different logic and needed no fixing.

mysql-test/r/subselect_mat.result

@@ -1999,6 +1999,20 @@ b	b	v	v
 b	b	s	s
 b	b	y	y
 DROP TABLE t1,t2;
+#
+# MDEV-4465: Reproducible crash (mysqld got signal 11) in multi_delete::initialize_tables with semijoin+materialization
+#
+CREATE TABLE t1 (
+id int(11) NOT NULL
+);
+CREATE TABLE t2 (
+id   int(11) NOT NULL,
+a_id int(11) DEFAULT NULL
+);
+insert into t1 values (1), (2), (3);
+insert into t2 values (1, 1), (2, 1), (3, 1), (4, 2), (5, 3), (6, 3), (7, 3);
+delete t2 from t2 where a_id in (select * from (select t1.id from t1 limit 2) as x);
+drop table t1,t2;
 # This must be at the end:
 set optimizer_switch=@subselect_sj_mat_tmp;
 set join_cache_level=@save_join_cache_level;

mysql-test/r/subselect_sj_mat.result

@@ -2039,6 +2039,20 @@ b	b	v	v
 b	b	s	s
 b	b	y	y
 DROP TABLE t1,t2;
+#
+# MDEV-4465: Reproducible crash (mysqld got signal 11) in multi_delete::initialize_tables with semijoin+materialization
+#
+CREATE TABLE t1 (
+id int(11) NOT NULL
+);
+CREATE TABLE t2 (
+id   int(11) NOT NULL,
+a_id int(11) DEFAULT NULL
+);
+insert into t1 values (1), (2), (3);
+insert into t2 values (1, 1), (2, 1), (3, 1), (4, 2), (5, 3), (6, 3), (7, 3);
+delete t2 from t2 where a_id in (select * from (select t1.id from t1 limit 2) as x);
+drop table t1,t2;
 # This must be at the end:
 set optimizer_switch=@subselect_sj_mat_tmp;
 set join_cache_level=@save_join_cache_level;

mysql-test/t/subselect_sj_mat.test

@@ -1677,6 +1677,25 @@ SELECT * FROM t1, t2 WHERE b1 IN ( SELECT b2 FROM t2 WHERE b1 > 'o' ) AND ( b1 <
 
 DROP TABLE t1,t2;
 
+--echo #
+--echo # MDEV-4465: Reproducible crash (mysqld got signal 11) in multi_delete::initialize_tables with semijoin+materialization
+--echo #
+CREATE TABLE t1 (
+  id int(11) NOT NULL
+);
+
+CREATE TABLE t2 (
+  id   int(11) NOT NULL,
+  a_id int(11) DEFAULT NULL
+);
+
+insert into t1 values (1), (2), (3);
+insert into t2 values (1, 1), (2, 1), (3, 1), (4, 2), (5, 3), (6, 3), (7, 3);
+
+delete t2 from t2 where a_id in (select * from (select t1.id from t1 limit 2) as x);
+
+drop table t1,t2;
+
 --echo # This must be at the end:
 set optimizer_switch=@subselect_sj_mat_tmp;
 set join_cache_level=@save_join_cache_level;

sql/sql_delete.cc

@@ -677,7 +677,7 @@ multi_delete::initialize_tables(JOIN *join)
        tab; 
        tab= next_linear_tab(join, tab, WITHOUT_BUSH_ROOTS))
   {
-    if (tab->table->map & tables_to_delete_from)
+    if (!tab->bush_children && tab->table->map & tables_to_delete_from)
     {
       /* We are going to delete from this table */
       TABLE *tbl=walk->table=tab->table;