Added tests if a user variable is changed in the same query.

Docs/manual.texi:
  Updated info about some common problems.
mysql-test/r/user_var.result:
  Added tests of using user variables.
mysql-test/t/user_var.test:
  Added tests of using user variables.

3 files changed, 12 insertions, 5 deletions

diff --git a/sql/item_func.cc b/sql/item_func.cc
index ef46a624aaf..61e64be1e74 100644
--- a/sql/item_func.cc
+++ b/sql/item_func.cc
@@ -1606,6 +1606,7 @@ static user_var_entry *get_variable(HASH *hash, LEX_STRING &name,
     entry->name.length=name.length;
     entry->value=0;
     entry->length=0;
+    entry->update_query_id=0;
     entry->type=STRING_RESULT;
     memcpy(entry->name.str, name.str, name.length+1);
     if (hash_insert(hash,(byte*) entry))
@@ -1625,6 +1626,7 @@ bool Item_func_set_user_var::fix_fields(THD *thd,TABLE_LIST *tables)
   if (Item_func::fix_fields(thd,tables) ||
       !(entry= get_variable(&thd->user_vars, name, 1)))
     return 1;
+  entry->update_query_id=thd->query_id;
   return 0;
 }
 
@@ -1809,10 +1811,12 @@ longlong Item_func_get_user_var::val_int()
 
 void Item_func_get_user_var::fix_length_and_dec()
 {
+  THD *thd=current_thd;
   maybe_null=1;
   decimals=NOT_FIXED_DEC;
   max_length=MAX_BLOB_WIDTH;
-  entry= get_variable(&current_thd->user_vars, name, 0);
+  if ((entry= get_variable(&thd->user_vars, name, 0)))
+    const_var_flag= thd->query_id != entry->update_query_id;
 }
 
 
diff --git a/sql/item_func.h b/sql/item_func.h
index 595329d4bf4..ac4c230f312 100644
--- a/sql/item_func.h
+++ b/sql/item_func.h
@@ -825,9 +825,11 @@ class Item_func_get_user_var :public Item_func
 {
   LEX_STRING name;
   user_var_entry *entry;
+  bool const_var_flag;
 
 public:
-  Item_func_get_user_var(LEX_STRING a): Item_func(), name(a) {}
+  Item_func_get_user_var(LEX_STRING a):
+    Item_func(), name(a), const_var_flag(1) {}
   user_var_entry *get_entry();
   double val();
   longlong val_int();
@@ -835,8 +837,9 @@ public:
   void fix_length_and_dec();
   enum Item_result result_type() const;
   const char *func_name() const { return "get_user_var"; }
-  bool const_item() const { return 0; }
-  table_map used_tables() const { return RAND_TABLE_BIT; }
+  bool const_item() const { return const_var_flag; }
+  table_map used_tables() const
+  { return const_var_flag ? 0 : RAND_TABLE_BIT; }
 };
 
 class Item_func_inet_aton : public Item_int_func
diff --git a/sql/sql_class.h b/sql/sql_class.h
index 37ef237757d..1b444598401 100644
--- a/sql/sql_class.h
+++ b/sql/sql_class.h
@@ -550,7 +550,7 @@ class user_var_entry
  public:
   LEX_STRING name;
   char *value;
-  ulong length;
+  ulong length, update_query_id;
   Item_result type;
 };