mysql 数据库group by 按排序取值
mysql 5.7 以后，group by 想要按照排序的顺序来取值，在子结果集中要有union,group by 等操作，不然按照id默认排序来取值
示例：
数据库：
score表
id user_id num
1 100 95
2 100 96
3 101 97
4 101 95
select * from score group by user_id order by num desc
结果
id user_id num
3 101 97
1 100 95
select * from
(select * from score group by id order by num desc) f
group by user_id order by num desc
结果
id user_id num
3 101 97
2 100 96