Make LEX::can_not_use_merged more general

sql/sql_lex.cc

@@ -4076,6 +4076,10 @@ bool LEX::can_use_merged()
   SYNOPSIS
     LEX::can_not_use_merged()
 
+  @param no_update_or_delete Set to 1 if we can't use merge with multiple-table
+                             updates, like when used from
+                             TALE_LIST::init_derived()
+
   DESCRIPTION
     Temporary table algorithm will be used on all SELECT levels for queries
     listed here (see also LEX::can_use_merged()).
@@ -4085,10 +4089,9 @@ bool LEX::can_use_merged()
     TRUE  - VIEWs with MERGE algorithms can be used
 */
 
-bool LEX::can_not_use_merged()
+bool LEX::can_not_use_merged(bool no_update_or_delete)
 {
-  switch (sql_command)
-  {
+  switch (sql_command) {
   case SQLCOM_CREATE_VIEW:
   case SQLCOM_SHOW_CREATE:
   /*
@@ -4098,6 +4101,13 @@ bool LEX::can_not_use_merged()
   */
   case SQLCOM_SHOW_FIELDS:
     return TRUE;
+
+  case SQLCOM_UPDATE_MULTI:
+  case SQLCOM_DELETE_MULTI:
+    if (no_update_or_delete)
+      return TRUE;
+    /* Fall through */
+
   default:
     return FALSE;
   }

sql/sql_lex.h

@@ -3641,7 +3641,7 @@ struct LEX: public Query_tables_list
 
   bool can_be_merged();
   bool can_use_merged();
-  bool can_not_use_merged();
+  bool can_not_use_merged(bool no_update_or_delete);
   bool only_view_structure();
   bool need_correct_ident();
   uint8 get_effective_with_check(TABLE_LIST *view);

sql/sql_view.cc

@@ -1687,7 +1687,7 @@ 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())
+        !old_lex->can_not_use_merged(0))
     {
       /* lex should contain at least one table */
       DBUG_ASSERT(view_main_select_tables != 0);

sql/table.cc

@@ -9341,9 +9341,7 @@ bool TABLE_LIST::init_derived(THD *thd, bool init_view)
     /* A subquery might be forced to be materialized due to a side-effect. */
     if (!is_materialized_derived() && first_select->is_mergeable() &&
         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) &&
+        !thd->lex->can_not_use_merged(1) &&
         !is_recursive_with_table())
       set_merged_derived();
     else