after review & some other fixes

mysql-test/r/subselect.result:
  after merge fix
sql/item_func.cc:
  fixed used_tables_cache
sql/item_func.h:
  fixed used_tables_cache
sql/sql_select.cc:
  removed != and !

mysql-test/r/subselect.result

@@ -1637,4 +1637,3 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
 2	UNCACHEABLE SUBQUERY	t1	system	NULL	NULL	NULL	NULL	1	
 drop table t1;
-

sql/item_func.cc

@@ -959,7 +959,6 @@ double Item_func_round::val()
   return tmp2;
 }
 
-
 void Item_func_rand::fix_length_and_dec()
 {
   decimals=NOT_FIXED_DEC; 
@@ -990,6 +989,12 @@ void Item_func_rand::fix_length_and_dec()
   }
 }
 
+void Item_func_rand::update_used_tables()
+{
+  Item_real_func::update_used_tables();
+  used_tables_cache|= RAND_TABLE_BIT;
+}
+
 
 double Item_func_rand::val()
 {

sql/item_func.h

@@ -512,6 +512,7 @@ class Item_func_rand :public Item_real_func
   double val();
   const char *func_name() const { return "rand"; }
   bool const_item() const { return 0; }
+  void update_used_tables();
   void fix_length_and_dec();
 };
 

sql/sql_select.cc

@@ -585,8 +585,9 @@ JOIN::optimize()
   }
   if (const_table_map != found_const_table_map &&
       !(select_options & SELECT_DESCRIBE) &&
-      !((conds->used_tables() & RAND_TABLE_BIT) &&
-	select_lex->master_unit() != &thd->lex->unit))// not upper level SELECT
+      (!conds ||
+       !(conds->used_tables() & RAND_TABLE_BIT) ||
+       select_lex->master_unit() == &thd->lex->unit)) // upper level SELECT
   {
     zero_result_cause= "no matching row in const table";
     DBUG_PRINT("error",("Error: %s", zero_result_cause));