MDEV-6251: SIGSEGV in query optimizer (in set_check_materialized with MERGE view)

mysql_derived_merge() made correctly working with views.

sql/sql_derived.cc

@@ -391,17 +391,13 @@ bool mysql_derived_merge(THD *thd, LEX *lex, TABLE_LIST *derived)
     if (parent_lex->get_free_table_map(&map, &tablenr))
     {
       /* There is no enough table bits, fall back to materialization. */
-      derived->change_refs_to_fields();
-      derived->set_materialized_derived();
-      goto exit_merge;
+      goto unconditional_materialization;
     }
 
     if (dt_select->leaf_tables.elements + tablenr > MAX_TABLES)
     {
       /* There is no enough table bits, fall back to materialization. */
-      derived->change_refs_to_fields();
-      derived->set_materialized_derived();
-      goto exit_merge;
+      goto unconditional_materialization;
     }
 
     if (dt_select->options & OPTION_SCHEMA_TABLE)
@@ -472,6 +468,15 @@ exit_merge:
   if (arena)
     thd->restore_active_arena(arena, &backup);
   DBUG_RETURN(res);
+
+unconditional_materialization:
+  derived->change_refs_to_fields();
+  derived->set_materialized_derived();
+  if (!derived->table || !derived->table->created)
+    res= mysql_derived_create(thd, lex, derived);
+  if (!res)
+    res= mysql_derived_fill(thd, lex, derived);
+  goto exit_merge;
 }
 
 

sql/table.cc

@@ -4441,6 +4441,10 @@ void TABLE_LIST::set_check_merged()
 
 void TABLE_LIST::set_check_materialized()
 {
+  DBUG_ENTER("TABLE_LIST::set_check_materialized");
+  SELECT_LEX_UNIT *derived= this->derived;
+  if (view)
+    derived= &view->unit;
   DBUG_ASSERT(derived);
   if (!derived->first_select()->exclude_from_table_unique_test)
     derived->set_unique_exclude();
@@ -4453,6 +4457,7 @@ void TABLE_LIST::set_check_materialized()
                 derived->first_select()->first_inner_unit()->first_select()->
                 exclude_from_table_unique_test);
   }
+  DBUG_VOID_RETURN;
 }
 
 TABLE *TABLE_LIST::get_real_join_table()

sql/table.h

@@ -1804,7 +1804,7 @@ struct TABLE_LIST
   void set_materialized_derived()
   {
     DBUG_ENTER("set_materialized_derived");
-    derived_type= ((derived_type & DTYPE_MASK) |
+    derived_type= ((derived_type & (derived ? DTYPE_MASK : DTYPE_VIEW)) |
                    DTYPE_TABLE | DTYPE_MATERIALIZE);
     set_check_materialized();
     DBUG_VOID_RETURN;