mysql随机取数据，如何实现高效率？

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