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。
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
我认为你应该对之前的查询进行修改:
SELECT UserId, Value FROM Users U1 WHERE
Date = ( SELECT MAX(Date) FROM Users where UserId = U1.UserId)
其他回答
select UserId,max(Date) over (partition by UserId) value from users;
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, MAX(value) KEEP (DENSE_RANK FIRST ORDER BY date DESC)
FROM table
GROUP BY userid
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
这应该非常简单:
SELECT UserId, Value
FROM Users u
WHERE Date = (SELECT MAX(Date) FROM Users WHERE UserID = u.UserID)