some code cleanup as per CTO's instructions plus a small bug fix with

a corresponding test case....

mysql-test/r/derived.result

@@ -37,3 +37,6 @@ select * from (select 1);
 select a from (select 1 as a);
 a
 1
+select 1 from (select 1);
+1
+1

mysql-test/t/derived.test

@@ -21,3 +21,4 @@ SELECT (SELECT 1) as a FROM (SELECT 1 FROM t1  HAVING a=1);
 drop table if exists  t1.t2,t3;
 select * from (select 1);
 select a from (select 1 as a);
+select 1 from (select 1);

sql/sql_derived.cc

@@ -118,7 +118,7 @@ int mysql_derived(THD *thd, LEX *lex, SELECT_LEX_UNIT *unit, TABLE_LIST *t)
 	  table->tmp_table=TMP_TABLE;
 	  if (!lex->describe)
 	    sl->exclude();
-	  t->db= (tables && tables->db && tables->db[0]) ? t->db : thd->db;
+	  t->db="";
 	  t->derived=(SELECT_LEX *)0; // just in case ...
 	}
       }

sql/sql_parse.cc

@@ -2717,7 +2717,7 @@ check_table_access(THD *thd, ulong want_access,TABLE_LIST *tables,
   TABLE_LIST *org_tables=tables;
   for (; tables ; tables=tables->next)
   {
-    if (tables->derived)
+    if (tables->derived || (tables->table && (int)tables->table->tmp_table))
       continue;
     if ((thd->master_access & want_access) == (want_access & ~EXTRA_ACL) &&
 	thd->db)
@@ -2735,7 +2735,7 @@ check_table_access(THD *thd, ulong want_access,TABLE_LIST *tables,
 	found=1;
       }
     }
-    else if (tables->db && check_access(thd,want_access,tables->db,&tables->grant.privilege,
+    else if (check_access(thd,want_access,tables->db,&tables->grant.privilege,
 			  0, no_errors))
       return TRUE;
   }