其他数据还是按排序取，只有指定字段获取到最大值

SELECT id, max(operat_time) FROM tb GROUP BY id;

其他数据还是按排序取，只有指定字段获取到最小值

SELECT id, min(operat_time) FROM tb GROUP BY id;

按操作用户uid分组查最新一条操作记录

select * from (select * from tb order by operat_time desc) as a group by a.uid

MySQL用GROUP BY分组取字段最大值或最新一条