表:
UserId, Value, Date.
我想获得UserId，为每个UserId的最大值(日期)的值。也就是说，具有最新日期的每个UserId的值。有没有一种方法可以在SQL中简单地做到这一点?(最好是Oracle)
更新:为任何歧义道歉:我需要得到所有的用户id。但是对于每个UserId，只有该用户拥有最新日期的行。
当前回答
答案是Oracle。这里有一个更复杂的SQL回答:
谁的整体作业成绩最好(作业点数最多)?
SELECT FIRST, LAST, SUM(POINTS) AS TOTAL
FROM STUDENTS S, RESULTS R
WHERE S.SID = R.SID AND R.CAT = 'H'
GROUP BY S.SID, FIRST, LAST
HAVING SUM(POINTS) >= ALL (SELECT SUM (POINTS)
FROM RESULTS
WHERE CAT = 'H'
GROUP BY SID)
还有一个更难的例子，需要一些解释，我没有时间了
给出2008年最受欢迎的书(ISBN和书名)，即2008年最常被借阅的书。
SELECT X.ISBN, X.title, X.loans
FROM (SELECT Book.ISBN, Book.title, count(Loan.dateTimeOut) AS loans
FROM CatalogEntry Book
LEFT JOIN BookOnShelf Copy
ON Book.bookId = Copy.bookId
LEFT JOIN (SELECT * FROM Loan WHERE YEAR(Loan.dateTimeOut) = 2008) Loan
ON Copy.copyId = Loan.copyId
GROUP BY Book.title) X
HAVING loans >= ALL (SELECT count(Loan.dateTimeOut) AS loans
FROM CatalogEntry Book
LEFT JOIN BookOnShelf Copy
ON Book.bookId = Copy.bookId
LEFT JOIN (SELECT * FROM Loan WHERE YEAR(Loan.dateTimeOut) = 2008) Loan
ON Copy.copyId = Loan.copyId
GROUP BY Book.title);
希望这能对(任何人)有所帮助。：）
问候 古斯
其他回答
SELECT a.userid,a.values1,b.mm
FROM table_name a,(SELECT userid,Max(date1)AS mm FROM table_name GROUP BY userid) b
WHERE a.userid=b.userid AND a.DATE1=b.mm;
select userid, value, date
from thetable t1 ,
( select t2.userid, max(t2.date) date2
from thetable t2
group by t2.userid ) t3
where t3.userid t1.userid and
t3.date2 = t1.date
恕我直言，这是可行的。HTH
检查这个链接，如果你的问题似乎类似的页面，然后我会建议你下面的查询，将给出该链接的解决方案
选择不同的sno,item_name,max(start_date) over(sno分区)，max(end_date) over(sno分区)，max(creation_date) over(sno分区)， Max (last_modified_date) over(sno分区) 从uniq_select_records 按sno,item_name asc排序;
是否会给出与该链接相关的准确结果
使用代码:
select T.UserId,T.dt from (select UserId,max(dt)
over (partition by UserId) as dt from t_users)T where T.dt=dt;
这将检索结果，而不考虑UserId的重复值。 如果你的UserId是唯一的，它变得更简单:
select UserId,max(dt) from t_users group by UserId;
我想这应该有用吧?
Select
T1.UserId,
(Select Top 1 T2.Value From Table T2 Where T2.UserId = T1.UserId Order By Date Desc) As 'Value'
From
Table T1
Group By
T1.UserId
Order By
T1.UserId
