Window functions: handle window functions as arguments to other functions

Window functions need to have their own column in the work (temp) table,
like aggregate functions do.
They don't need val_int() -> val_int_result() conversion though, so they
should be wrapped with Item_direct_ref, not Item_aggregate_ref.

mysql-test/r/win.result

@@ -1812,3 +1812,22 @@ s1	s2	X
 NULL	a	2
 NULL	NULL	1
 drop table t1;
+#
+# Try window functions that are not directly present in the select list
+#
+create table t1 (a int, b int);
+insert into t1 values 
+(1,3),
+(2,2),
+(3,1);
+select 
+rank() over (order by a) -
+rank() over (order by b)
+from
+t1;
+rank() over (order by a) -
+rank() over (order by b)
+0
+0
+0
+drop table t1;

mysql-test/t/win.test

@@ -1096,3 +1096,20 @@ select *, row_number() over (order by s1, s2) as X from t1 order by X desc;
 select *, row_number() over (order by s1, s2) as X from t1 order by X desc;
 drop table t1;
 
+--echo #
+--echo # Try window functions that are not directly present in the select list
+--echo #
+create table t1 (a int, b int);
+insert into t1 values 
+  (1,3),
+  (2,2),
+  (3,1);
+
+select 
+  rank() over (order by a) -
+  rank() over (order by b)
+from
+  t1;
+
+drop table t1;
+

sql/item.cc

@@ -1761,6 +1761,14 @@ void Item::split_sum_func2(THD *thd, Ref_ptr_array ref_pointer_array,
         ((Item_sum *) this)->ref_by)
       return;
   }
+  else if (type() == WINDOW_FUNC_ITEM)
+  {
+    /*
+      Skip the else part, window functions are very special functions: 
+      they need to have their own fields in the temp. table, but they
+      need to be proceessed differently than regular aggregate functions
+    */
+  }
   else
   {
     /* Not a SUM() function */
@@ -1801,7 +1809,7 @@ void Item::split_sum_func2(THD *thd, Ref_ptr_array ref_pointer_array,
     Exception is Item_direct_view_ref which we need to convert to
     Item_ref to allow fields from view being stored in tmp table.
   */
-  Item_aggregate_ref *item_ref;
+  Item_ref *item_ref;
   uint el= fields.elements;
   /*
     If this is an item_ref, get the original item
@@ -1811,13 +1819,24 @@ void Item::split_sum_func2(THD *thd, Ref_ptr_array ref_pointer_array,
   Item *real_itm= real_item();
 
   ref_pointer_array[el]= real_itm;
-  if (!(item_ref= (new (thd->mem_root)
+  if (type() == WINDOW_FUNC_ITEM)
-                   Item_aggregate_ref(thd,
+  {
-                                      &thd->lex->current_select->context,
+    if (!(item_ref= (new (thd->mem_root)
-				      &ref_pointer_array[el], 0, name))))
+                     Item_direct_ref(thd,
-    return;                                   // fatal_error is set
+                                        &thd->lex->current_select->context,
+                                        &ref_pointer_array[el], 0, name))))
+      return;                                   // fatal_error is set
+  }
+  else
+  {
+    if (!(item_ref= (new (thd->mem_root)
+                     Item_aggregate_ref(thd,
+                                        &thd->lex->current_select->context,
+                                        &ref_pointer_array[el], 0, name))))
+      return;                                   // fatal_error is set
+  }
   if (type() == SUM_FUNC_ITEM)
-    item_ref->depended_from= ((Item_sum *) this)->depended_from(); 
+    item_ref->depended_from= ((Item_sum *) this)->depended_from();
   fields.push_front(real_itm);
   thd->change_item_tree(ref, item_ref);
 }

sql/sql_base.cc

@@ -7911,7 +7911,7 @@ bool setup_fields(THD *thd, Ref_ptr_array ref_pointer_array,
       Item_window_func::split_sum_func.
     */
     if ((item->with_sum_func && item->type() != Item::SUM_FUNC_ITEM &&
-	 sum_func_list) || item->type() == Item::WINDOW_FUNC_ITEM)
+	 sum_func_list) || item->with_window_func)
       item->split_sum_func(thd, ref_pointer_array, *sum_func_list,
                            SPLIT_SUM_SELECT);
     thd->lex->current_select->select_list_tables|= item->used_tables();