MDEV-15744: Assertion `derived->table' failed in mysql_derived_merge_for_insert

For singe-table views, we need to find the bottom most base table in the embedded views
and then update that table

mysql-test/r/loaddata.result

@@ -550,3 +550,27 @@ SELECT HEX(a) FROM t1;
 HEX(a)
 C3A4
 DROP TABLE t1;
+#
+# MDEV-15744: Assertion `derived->table' failed in mysql_derived_merge_for_insert
+#
+create table t1 (a int, b int);
+CREATE OR REPLACE VIEW t2 AS SELECT * FROM t1;
+CREATE VIEW v2 AS SELECT * FROM t2;
+LOAD DATA INFILE '../../std_data/loaddata7.dat' INTO TABLE v2
+FIELDS TERMINATED BY ',' LINES TERMINATED BY '\r\n';
+select * from v2;
+a	b
+2	2
+3	3
+4	4
+5	5
+6	6
+select * from t2;
+a	b
+2	2
+3	3
+4	4
+5	5
+6	6
+DROP VIEW IF EXISTS v2,t2;
+DROP TABLE IF EXISTS t1;

mysql-test/t/loaddata.test

@@ -676,3 +676,17 @@ CREATE TABLE t1 (a VARCHAR(10) CHARACTER SET utf8);
 LOAD DATA INFILE '../../std_data/loaddata/mdev-11631.txt' INTO TABLE t1 CHARACTER SET utf8;
 SELECT HEX(a) FROM t1;
 DROP TABLE t1;
+
+--echo #
+--echo # MDEV-15744: Assertion `derived->table' failed in mysql_derived_merge_for_insert
+--echo #
+
+create table t1 (a int, b int);
+CREATE OR REPLACE VIEW t2 AS SELECT * FROM t1;
+CREATE VIEW v2 AS SELECT * FROM t2;
+LOAD DATA INFILE '../../std_data/loaddata7.dat' INTO TABLE v2
+     FIELDS TERMINATED BY ',' LINES TERMINATED BY '\r\n';
+select * from v2;
+select * from t2;
+DROP VIEW IF EXISTS v2,t2;
+DROP TABLE IF EXISTS t1;

sql/sql_load.cc

@@ -233,8 +233,9 @@ int mysql_load(THD *thd,sql_exchange *ex,TABLE_LIST *table_list,
 
   if (open_and_lock_tables(thd, table_list, TRUE, 0))
     DBUG_RETURN(TRUE);
-  if (mysql_handle_single_derived(thd->lex, table_list, DT_MERGE_FOR_INSERT) ||
-      mysql_handle_single_derived(thd->lex, table_list, DT_PREPARE))
+  if (table_list->handle_derived(thd->lex, DT_MERGE_FOR_INSERT))
+    DBUG_RETURN(TRUE);
+  if (mysql_handle_list_of_derived(thd->lex, table_list, DT_PREPARE))
     DBUG_RETURN(TRUE);
   if (setup_tables_and_check_access(thd, &thd->lex->select_lex.context,
                                     &thd->lex->select_lex.top_join_list,