Fix bug #12922 if(sum(),...) with group from view returns wrong results

Fields of view represented by Item_direct_view_ref. When complex expression
such as if(sum()>...,...) is splited in simpler parts by refs was ignored.
Beside this direct ref doesn't use it's result_field and thus can't store
it's result in tmp table which is needed for sum() ... group.
All this results in reported bug.

Item::split_sum_func2() now converts Item_direct_view_ref to Item_ref to
make fields from view being storable in tmp table.

mysql-test/r/view.result

@@ -2151,3 +2151,12 @@ select * from v1;
 strcmp(f1,'a')
 drop view v1;
 drop table t1;
+create table t1 (f1 int, f2 int,f3 int);
+insert into t1 values (1,10,20),(2,0,0);
+create view v1 as select * from t1;
+select if(sum(f1)>1,f2,f3) from v1 group by f1;
+if(sum(f1)>1,f2,f3)
+20
+0
+drop view v1;
+drop table t1;

mysql-test/t/view.test

@@ -2018,3 +2018,13 @@ create view v1 as select strcmp(f1,'a') from t1;
 select * from v1;
 drop view v1;
 drop table t1;
+
+#
+# Bug #12922 if(sum(),...) with group from view returns wrong results 
+#
+create table t1 (f1 int, f2 int,f3 int);
+insert into t1 values (1,10,20),(2,0,0);
+create view v1 as select * from t1;
+select if(sum(f1)>1,f2,f3) from v1 group by f1;
+drop view v1;
+drop table t1;

sql/item.cc

@@ -1022,9 +1022,9 @@ void Item::split_sum_func2(THD *thd, Item **ref_pointer_array,
     /* Will split complicated items and ignore simple ones */
     split_sum_func(thd, ref_pointer_array, fields);
   }
-  else if ((type() == SUM_FUNC_ITEM ||
-            (used_tables() & ~PARAM_TABLE_BIT)) &&
-           type() != REF_ITEM)
+  else if ((type() == SUM_FUNC_ITEM || (used_tables() & ~PARAM_TABLE_BIT)) &&
+           (type() != REF_ITEM ||
+           ((Item_ref*)this)->ref_type() == Item_ref::VIEW_REF))
   {
     /*
       Replace item with a reference so that we can easily calculate
@@ -1033,15 +1033,17 @@ void Item::split_sum_func2(THD *thd, Item **ref_pointer_array,
       The test above is to ensure we don't do a reference for things
       that are constants (PARAM_TABLE_BIT is in effect a constant)
       or already referenced (for example an item in HAVING)
+      Exception is Item_direct_view_ref which we need to convert to
+      Item_ref to allow fields from view being stored in tmp table.
     */
     uint el= fields.elements;
-    Item *new_item;    
-    ref_pointer_array[el]= this;
+    Item *new_item, *real_item= real_item();
+
+    ref_pointer_array[el]= real_item;
     if (!(new_item= new Item_ref(&thd->lex->current_select->context,
                                  ref_pointer_array + el, 0, name)))
       return;                                   // fatal_error is set
-    fields.push_front(this);
-    ref_pointer_array[el]= this;
+    fields.push_front(real_item);
     thd->change_item_tree(ref, new_item);
   }
 }

sql/item.h

@@ -1537,6 +1537,7 @@ class Item_ref :public Item_ident
 protected:
   void set_properties();
 public:
+  enum Ref_Type { REF, DIRECT_REF, VIEW_REF };
   Field *result_field;			 /* Save result here */
   Item **ref;
   Item_ref(Name_resolution_context *context_arg,
@@ -1617,6 +1618,7 @@ class Item_ref :public Item_ident
   void cleanup();
   Item_field *filed_for_view_update()
     { return (*ref)->filed_for_view_update(); }
+  virtual Ref_Type ref_type() { return REF; }
 };
 
 
@@ -1641,6 +1643,7 @@ class Item_direct_ref :public Item_ref
   bool val_bool();
   bool is_null();
   bool get_date(TIME *ltime,uint fuzzydate);
+  virtual Ref_Type ref_type() { return DIRECT_REF; }
 };
 
 /*
@@ -1660,6 +1663,7 @@ class Item_direct_view_ref :public Item_direct_ref
 
   bool fix_fields(THD *, Item **);
   bool eq(const Item *item, bool binary_cmp) const;
+  virtual Ref_Type ref_type() { return VIEW_REF; }
 };