MDEV-31162 Crash for query using ROWNUM over multi-table view with ORDER BY

This bug could cause a crash of the server when processing a query with
ROWNUM() if it used in its FROM list a reference to a mergeable view
defined as SELECT over more than one table that contained ORDER BY clause.
When a mergeable view with ORDER BY clause and without LIMIT clause is used
in the FROM list of a query that does not have ORDER BY clause the ORDER BY
clause of the view is moved to the query. The code that performed this
transformation forgot to delete the moved ORDER BY list from the view.
If a query contains ROWNUM() and uses a mergeable multi-table view with
ORDER BY then according to the current code of TABLE_LIST::init_derived()
the view has to be forcibly materialized. As the query and the view shared
the same items in its ORDER BY lists they could not be properly resolved
either in the query or in the view. This led to a crash of the server.

This patch has returned back the original signature of LEX::can_not_use_merged()
to comply with 10.4 code of the condition that checks whether a megeable
view has to be forcibly materialized.

Approved by Oleksandr Byelkin <sanja@mariadb.com>

mysql-test/main/derived_view.result

@@ -4190,4 +4190,52 @@ Warnings:
 Warning	1287	'@@big_tables' is deprecated and will be removed in a future release
 drop view v;
 drop table t1, t2;
+#
+# MDEV-31162: multi-table mergeable view with ORDER BY used
+#             in query with rownum() in WHERE
+#
+create table t1 (a INT) engine=MyISAM;
+insert into t1 values (1),(2);
+create table t2 (b INT) engine=MyISAM;
+insert into t2 values (3),(4);
+create view v1 AS select * from t1 join t2 order by b;
+explain select * from v1 where rownum() <= 2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	Using temporary; Using filesort
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	2	Using where; Using join buffer (flat, BNL join)
+select * from v1 where rownum() <= 2;
+a	b
+1	3
+2	3
+prepare stmt from "select * from v1 where rownum() <= 2";
+execute stmt;
+a	b
+1	3
+2	3
+execute stmt;
+a	b
+1	3
+2	3
+deallocate prepare stmt;
+create view v2 AS select * from t1 join t2 order by b/a;
+explain select * from v2 where rownum() <= 2;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	Using temporary; Using filesort
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	2	Using where; Using join buffer (flat, BNL join)
+select * from v2 where rownum() <= 2;
+a	b
+2	3
+1	3
+prepare stmt from "select * from v2 where rownum() <= 2";
+execute stmt;
+a	b
+2	3
+1	3
+execute stmt;
+a	b
+2	3
+1	3
+deallocate prepare stmt;
+drop view v1,v2;
+drop table t1,t2;
 # End of 10.6 tests

mysql-test/main/derived_view.test

@@ -2773,4 +2773,44 @@ set big_tables=default;
 drop view v;
 drop table t1, t2;
 
+--echo #
+--echo # MDEV-31162: multi-table mergeable view with ORDER BY used
+--echo #             in query with rownum() in WHERE
+--echo #
+
+create table t1 (a INT) engine=MyISAM;
+insert into t1 values (1),(2);
+
+create table t2 (b INT) engine=MyISAM;
+insert into t2 values (3),(4);
+
+create view v1 AS select * from t1 join t2 order by b;
+let $q1=
+select * from v1 where rownum() <= 2;
+
+eval explain $q1;
+--sorted_result
+eval $q1;
+
+eval prepare stmt from "$q1";
+--sorted_result
+execute stmt;
+--sorted_result
+execute stmt;
+deallocate prepare stmt;
+
+create view v2 AS select * from t1 join t2 order by b/a;
+let $q2=
+select * from v2 where rownum() <= 2;
+
+eval explain $q2;
+eval $q2;
+eval prepare stmt from "$q2";
+execute stmt;
+execute stmt;
+deallocate prepare stmt;
+
+drop view v1,v2;
+drop table t1,t2;
+
 --echo # End of 10.6 tests

sql/sql_lex.cc

@@ -4090,7 +4090,7 @@ bool LEX::can_use_merged()
     TRUE  - VIEWs with MERGE algorithms can be used
 */
 
-bool LEX::can_not_use_merged(bool no_update_or_delete)
+bool LEX::can_not_use_merged()
 {
   switch (sql_command) {
   case SQLCOM_CREATE_VIEW:
@@ -4103,10 +4103,6 @@ bool LEX::can_not_use_merged(bool no_update_or_delete)
   case SQLCOM_SHOW_FIELDS:
     return TRUE;
 
-  case SQLCOM_UPDATE_MULTI:
-  case SQLCOM_DELETE_MULTI:
-    return no_update_or_delete;
-
   default:
     return FALSE;
   }

sql/sql_lex.h

@@ -3659,7 +3659,7 @@ struct LEX: public Query_tables_list
 
   bool can_be_merged();
   bool can_use_merged();
-  bool can_not_use_merged(bool no_update_or_delete);
+  bool can_not_use_merged();
   bool only_view_structure();
   bool need_correct_ident();
   uint8 get_effective_with_check(TABLE_LIST *view);

sql/sql_view.cc

@@ -1808,7 +1808,7 @@ bool mysql_make_view(THD *thd, TABLE_SHARE *share, TABLE_LIST *table,
     if (view_is_mergeable &&
         (table->select_lex->master_unit() != &old_lex->unit ||
          old_lex->can_use_merged()) &&
-        !old_lex->can_not_use_merged(0))
+        !old_lex->can_not_use_merged())
     {
       /* lex should contain at least one table */
       DBUG_ASSERT(view_main_select_tables != 0);
@@ -1841,8 +1841,11 @@ bool mysql_make_view(THD *thd, TABLE_SHARE *share, TABLE_LIST *table,
       */
       if (!table->select_lex->master_unit()->is_unit_op() &&
           table->select_lex->order_list.elements == 0)
+      {
         table->select_lex->order_list.
           push_back(&lex->first_select_lex()->order_list);
+        lex->first_select_lex()->order_list.empty();
+      }
       else
       {
         if (old_lex->sql_command == SQLCOM_SELECT &&

sql/table.cc

@@ -9551,8 +9551,10 @@ bool TABLE_LIST::init_derived(THD *thd, bool init_view)
          (!first_select->group_list.elements &&
           !first_select->order_list.elements)) &&
         (is_view() ||
-         (optimizer_flag(thd, OPTIMIZER_SWITCH_DERIVED_MERGE) &&
-          !thd->lex->can_not_use_merged(1))) &&
+         optimizer_flag(thd, OPTIMIZER_SWITCH_DERIVED_MERGE)) &&
+          !thd->lex->can_not_use_merged() &&
+        !((thd->lex->sql_command == SQLCOM_UPDATE_MULTI ||
+           thd->lex->sql_command == SQLCOM_DELETE_MULTI) && !is_view()) &&
         !is_recursive_with_table())
       set_merged_derived();
     else