sql查询语句优化

一、sql语句随机取一条数据
例1：select * from vdn_delivery_order ORDER BY RAND() LIMIT 1;
例2：SELECT * FROM vdn_delivery_order v1 JOIN (SELECT RAND()*(SELECT max(id) FROM vdn_delivery_order) AS nid) v2 ON v1.id > v2.nid LIMIT 1;
说明：例1会进行全表扫描，当数据量大时，很耗时；例2先对ID随机再连表查询，查询效率更高
资料：MySQL优化之对RAND()的优化方法