SQL热题266难！！！求解答！！
标准答案是这样的：
select u.name, c.name, l.date from
user as u join login as l on u.id = l.user_id
join client as c on c.id = l.client_id
where (l.user_id, l.date) in
(
select user_id, max(date) from login
group by user_id
)
group by u.name, c.name, l.date
order by u.name ASC
那么为什么下面这样的解法就是错误的呢？
select u.name as u_n, c.name as c_n, max(l.date) as d from
login as l join user as u on l.user_id=u.id
join client as c on l.client_id=c.id
group by u.name
order by u.name asc
#笔试#
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