mysql随机获取优化话语

mysql随机获取优化语句
在网上找了一个随机取数语句，结合了自己的需求，运行出错，
看了半天没发现出错的地方，求指点

<br />$str="select * from dizhi where shijiancuo>'$times' GROUP BY user HAVING COUNT(user) > 4 AS t1 <br />JOIN (SELECT ROUND(RAND() * (SELECT MAX(id) FROM dizhi)) AS id) AS t2 <br />WHERE t1.id >= t2.id <br />ORDER BY t1.id ASC LIMIT 1" ;<br /><br /><br /><br />

------解决方案--------------------
select * from
 (select * from dizhi where shijiancuo>'$times' GROUP BY user HAVING COUNT(user) > 4) AS t1 
 JOIN
 (SELECT ROUND(RAND() * (SELECT MAX(id) FROM dizhi)) AS id) AS t2 
 WHERE t1.id >= t2.id 
 ORDER BY t1.id ASC LIMIT 1