Row item fixing (SCRUM related)

Inserted comment

sql/item_row.cc

@@ -18,8 +18,10 @@
 #include "assert.h"
 
 Item_row::Item_row(List<Item> &arg):
-  Item(), array_holder(1)
+  Item(), array_holder(1), used_tables_cache(0), const_item_cache(1)
 {
+
+  //TODO: think placing 2-3 component items in item (as it done for function)
   if ((arg_count= arg.elements))
     items= (Item**) sql_alloc(sizeof(Item*)*arg_count);
   else
@@ -45,16 +47,31 @@ void Item_row::illegal_method_call(const char *method)
 
 bool Item_row::fix_fields(THD *thd, TABLE_LIST *tabl, Item **ref)
 {
-  tables= 0;
+  null_value= 0;
+  maybe_null= 0;
   for (uint i= 0; i < arg_count; i++)
   {
     if (items[i]->fix_fields(thd, tabl, items+i))
       return 1;
-    tables |= items[i]->used_tables();
+    used_tables_cache |= items[i]->used_tables();
+    const_item_cache&= items[i]->const_item();
+    maybe_null|= items[i]->maybe_null;
   }
   return 0;
 }
 
+void Item_row::update_used_tables()
+{
+  used_tables_cache= 0;
+  const_item_cache= 1;
+  for (uint i= 0; i < arg_count; i++)
+  {
+    items[i]->update_used_tables();
+    used_tables_cache|= items[i]->used_tables();
+    const_item_cache&= items[i]->const_item();
+  }
+}
+
 bool Item_row::check_cols(uint c)
 {
   if (c != arg_count)

sql/item_row.h

@@ -17,13 +17,17 @@
 class Item_row: public Item
 {
   bool array_holder;
-  table_map tables;
+  table_map used_tables_cache;
+  bool const_item_cache;
   uint arg_count;
   Item **items;
 public:
   Item_row(List<Item> &);
   Item_row(Item_row *item):
-    Item(), array_holder(0), tables(item->tables), arg_count(item->arg_count),
+    Item(), array_holder(0), 
+    used_tables_cache(item->used_tables_cache),
+    const_item_cache(item->const_item_cache),
+    arg_count(item->arg_count),
     items(item->items)
   {}
 
@@ -56,8 +60,10 @@ public:
     return 0;
   };
   bool fix_fields(THD *thd, TABLE_LIST *tables, Item **ref);
-  table_map used_tables() const { return tables; };
+  table_map used_tables() const { return used_tables_cache; };
+  bool const_item() const { return const_item_cache; };
   enum Item_result result_type() const { return ROW_RESULT; }
+  void update_used_tables();
 
   virtual uint cols() { return arg_count; }
   virtual Item* el(uint i) { return items[i]; }

sql/sql_select.cc

@@ -763,6 +763,16 @@ JOIN::exec()
 			   select_options, unit)))
       DBUG_VOID_RETURN;
 
+    /*
+      We don't have to store rows in temp table that doesn't match HAVING if:
+      - we are sorting the table and writing complete group rows to the
+        temp table.
+      - We are using DISTINCT without resolving the distinct as a GROUP BY
+        on all columns.
+      
+      If having is not handled here, it will be checked before the row
+      is sent to the client.
+    */
     if (having_list && 
 	(sort_and_group || (exec_tmp_table->distinct && !group_list)))
       having=having_list;