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

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$str="select * from dizhi where shijiancuo>'$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 />

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