Mysql Group By、limit、where

1.Mysql执行顺序

写的顺序：select … from… where…. group by… having… order by..
执行顺序：from… where…group by… having…. select … order by…

按name分组查最新一条操作记录
select * from (select * from a order by time desc) as b group by b.name
指定字段获取最大值 
SELECT id, max(operat_time) FROM tb GROUP BY id;

# 推荐使用
select cluesTaracking_id,cluesId,
MAX(trackingTime),
fail_why from cluestracking
group by cluesId
order by trackingTime desc

参考连接

分组后统计其他字段(也需去重)

select
	date_format(create_time, '%Y-%m-%d') date_,
	count(distinct user_id) counts
from
	a
where
	del_ = 1
group by
		date_
order by
	date_ desc