mysql随机取数据，怎么实现高效率

SELECT sh1.* FROM fw_share AS sh1 JOIN (SELECT 	ROUND(		RAND() * ((SELECT MAX(share_id) FROM fw_share)-(SELECT MIN(share_id) FROM fw_share)) 		+ (SELECT MIN(share_id) FROM fw_share)	) AS share_id) AS sh2 WHERE sh1.share_id>=sh2.share_id

?

http://my.oschina.net/sharephper/blog/100104