MySQL的union和order by一起使用的问题

想使用下面的sql逻辑，会报错，
[Err] 1221 - Incorrect usage of UNION and ORDER BY

SELECT DISTINCT            APP_NAME        FROM            tm_platform_usr_reld        WHERE            app_id <> 'APP_ALL'        AND APP_NAME <> ''        ORDER BY            NEW_USR_CNT DESCUNION    SELECT DISTINCT        app_name    FROM        tm_platform_req_reld    WHERE        app_id <> 'APP_ALL'    AND APP_NAME <> ''

可以变通一下，

SELECT    *FROM    (        SELECT DISTINCT            APP_NAME        FROM            tm_platform_usr_reld        WHERE            app_id <> 'APP_ALL'        AND APP_NAME <> ''        ORDER BY            NEW_USR_CNT DESC    ) AS aUNION    SELECT DISTINCT        app_name    FROM        tm_platform_req_reld    WHERE        app_id <> 'APP_ALL'    AND APP_NAME <> ''

这样就可以使用了