I need your help to optimize the query to avoid using "Using filesort".The job of the query is to select all the articles that belongs to specific tag. The query is: "select title from tag,article where tag='Riyad' AND tag.article_id=article.id order by tag.article_id". the tables structure are the following:

Tag table

 CREATE TABLE `tag` (
 `tag` VARCHAR( 30 ) NOT NULL ,
 `article_id` INT NOT NULL ,
 INDEX ( `tag` )
 ) ENGINE = MYISAM ;

Article table

 CREATE TABLE `article` (
 `id` INT NOT NULL AUTO_INCREMENT PRIMARY KEY ,
 `title` VARCHAR( 60 ) NOT NULL
 ) ENGINE = MYISAM 

Sample data

 INSERT INTO `article` VALUES (1, 'About Riyad');
 INSERT INTO `article` VALUES (2, 'About Newyork');
 INSERT INTO `article` VALUES (3, 'About Paris');
 INSERT INTO `article` VALUES (4, 'About London');

 INSERT INTO `tag` VALUES ('Riyad', 1);
 INSERT INTO `tag` VALUES ('Saudia', 1);
 INSERT INTO `tag` VALUES ('Newyork', 2);
 INSERT INTO `tag` VALUES ('USA', 2);
 INSERT INTO `tag` VALUES ('Paris', 3);
 INSERT INTO `tag` VALUES ('France', 3);