TABLE::update_virtual_field to compute just one vcol

will be used later by storage engines (e.g. in MyISAM repair or in
InnoDB purge)

sql/item.cc

@@ -985,6 +985,18 @@ bool Item_field::check_field_expression_processor(void *arg)
   return 0;
 }
 
+bool Item_field::update_vcol_processor(void *arg)
+{
+  MY_BITMAP *map= (MY_BITMAP *) arg;
+  if (field->vcol_info &&
+      !bitmap_fast_test_and_set(map, field->field_index))
+  {
+    field->vcol_info->expr_item->walk(&Item::update_vcol_processor, 0, arg);
+    field->vcol_info->expr_item->save_in_field(field, 0);
+  }
+  return 0;
+}
+
 
 bool Item::check_cols(uint c)
 {

sql/item.h

@@ -1635,6 +1635,7 @@ class Item: public Value_source,
     timezone-dependent expressions in a (sub)partitioning function.
   */
   virtual bool check_valid_arguments_processor(void *arg) { return 0; }
+  virtual bool update_vcol_processor(void *arg) { return 0; }
   /*============== End of Item processor list ======================*/
 
   virtual Item *get_copy(THD *thd, MEM_ROOT *mem_root)=0;
@@ -2580,6 +2581,7 @@ class Item_field :public Item_ident
   bool enumerate_field_refs_processor(void *arg);
   bool update_table_bitmaps_processor(void *arg);
   bool switch_to_nullable_fields_processor(void *arg);
+  bool update_vcol_processor(void *arg);
   bool check_vcol_func_processor(void *arg)
   {
     return mark_unsupported_function(field_name, arg, VCOL_FIELD_REF);
@@ -5091,6 +5093,7 @@ class Item_default_value : public Item_field
   }
   table_map used_tables() const { return (table_map)0L; }
   Item_field *field_for_view_update() { return 0; }
+  bool update_vcol_processor(void *arg) { return 0; }
 
   bool walk(Item_processor processor, bool walk_subquery, void *args)
   {
@@ -5170,6 +5173,7 @@ class Item_insert_value : public Item_field
 	    (this->*processor)(args);
   }
   bool check_partition_func_processor(void *int_arg) {return TRUE;}
+  bool update_vcol_processor(void *arg) { return 0; }
   bool check_vcol_func_processor(void *arg)
   {
     return mark_unsupported_function("values()", arg, VCOL_IMPOSSIBLE);

sql/table.cc

@@ -7333,6 +7333,18 @@ int TABLE::update_virtual_fields(enum_vcol_update_mode update_mode)
   DBUG_RETURN(0);
 }
 
+int TABLE::update_virtual_field(Field *vf)
+{
+  DBUG_ENTER("TABLE::update_virtual_field");
+
+  in_use->reset_arena_for_cached_items(expr_arena);
+  bitmap_clear_all(&tmp_set);
+  vf->vcol_info->expr_item->walk(&Item::update_vcol_processor, 0, &tmp_set);
+  vf->vcol_info->expr_item->save_in_field(vf, 0);
+  in_use->reset_arena_for_cached_items(0);
+  DBUG_RETURN(0);
+}
+
 
 /**
   Update all DEFAULT and/or ON INSERT fields.

sql/table.h

@@ -1423,6 +1423,7 @@ struct TABLE
 
   uint actual_n_key_parts(KEY *keyinfo);
   ulong actual_key_flags(KEY *keyinfo);
+  int update_virtual_field(Field *vf);
   int update_virtual_fields(enum_vcol_update_mode update_mode);
   int update_default_fields(bool update, bool ignore_errors);
   void reset_default_fields();