support 'parallel' updates and rallback of whole statement in case of error in evalueting value which should be assigned

(BUG#1484)


mysql-test/r/variables.result:
  test of swaping variables
mysql-test/t/variables.test:
  test of swaping variables
sql/item_func.cc:
  new method of user variables to pre-fetch value
sql/item_func.h:
  new method of user variables to pre-fetch value
sql/set_var.cc:
  check() methods fetch & store value
sql/set_var.h:
  check() methods fetch & store value

1 files changed, 9 insertions, 0 deletions

diff --git a/sql/item_func.h b/sql/item_func.h
index 8086e65786d..fe9c2645216 100644
--- a/sql/item_func.h
+++ b/sql/item_func.h
@@ -900,6 +900,14 @@ class Item_func_set_user_var :public Item_func
   user_var_entry *entry;
   char buffer[MAX_FIELD_WIDTH];
   String value;
+  union
+  {
+    longlong vint;
+    double vreal;
+    String *vstr;
+  } save_result;
+  String save_buff;
+  
 
 public:
   Item_func_set_user_var(LEX_STRING a,Item *b)
@@ -910,6 +918,7 @@ public:
   String *val_str(String *str);
   bool update_hash(void *ptr, uint length, enum Item_result type, 
   		   CHARSET_INFO *cs, Derivation dv);
+  bool check();
   bool update();
   enum Item_result result_type () const { return cached_result_type; }
   bool fix_fields(THD *thd, struct st_table_list *tables, Item **ref);