mysql联合查询是用DISTINCT和GROUP BY之间的性能区别

在开发过程中遇到的问题：

有两张表，登录记录表和IP归属表

需求：查询某个地区和某个时间段登录的记录
有登录表有4000条数据，IP归属表有400条数据

用GROUP BY查询结果

SELECT * FROM login_log WHERE acctLoginIP IN (SELECT ip FROM ip_geolocation WHERE 
region LIKE '%西藏%' GROUP BY ip) AND acctLoginTime BETWEEN '2014-10-01 00:00:00' AND '2014-12-25 23:59:59' LIMIT 10;

结果用时4秒左右

用DISTINCT

SELECT * FROM login_log WHERE acctLoginIP IN (SELECT DISTINCT ip FROM ip_geolocation WHERE 
region LIKE '%西藏%') AND acctLoginTime BETWEEN '2014-10-01 00:00:00' AND '2014-12-25 23:59:59' LIMIT 10;

结果用时0.005秒左右

有登录表有4000条数据