select * from xxx order by rand() limit 1000
执行速度:0.444315
select * from xxxx where fid >= (select floor(rand() * ((select MAX(fid) from xxxx)-(select MIN(fid) from xxxx))+(select MIN(fid) from xxxx))) order by fid limit 1000
执行速度:0.049867
SELECT * FROM `xxxx` AS t1 JOIN (SELECT ROUND(RAND() * ((SELECT MAX(fid) FROM `xxxx`)-(SELECT MIN(fid) FROM `xxxx`))+(SELECT MIN(fid) FROM `xxxx`)) AS fid) AS t2 WHERE t1.fid >= t2.fid ORDER BY t1.fid LIMIT 1000