SQL：从其他表的每一行获取最后一个（最大）记录

Question

这里是我的表如下记录（GROUP BY）： （我目前使用SQL Server 2008）

YearLevels

YearLevelID  YearLevelName 
1    Freshman  
2    Sophomore  
3    Junior  
4    Senior 

学生

StudentID  FirstName  LastName 
1    John   Doe 
2    Peter   Pan 
3    Mark   Twain 

水平sAttained

SSID  StudentID YearLevelID 
1  1   2 
2  1   1 
3  1   3 
4  2   2 
5  3   1 
6  2   1 

输出应该是：

FullName  YearLevelName 
John Doe  Junior 
Peter Pan Sophomore 
Mark Twain Freshman 

Answer 1

SELECT FirstName + ' ' + LastName AS FullName, YearLevelName 
FROM Students S 
INNER JOIN (
    SELECT StudentID, MAX(YearLevelID) AS MaxLevel 
    FROM LevelsAttained 
    GROUP BY StudentID 
) MaxLevels ON MaxLevels.StudentID = S.StudentID 
INNER JOIN YearLevels Y ON Y.YearLevelID = MaxLevels.MaxLevel 

Answer 2

试试这个：

SELECT FirstName || ' ' || LastName AS FullName, l.YearLevelName AS YearLevelName 
FROM Students s 
JOIN (SELECT StudentID, MAX(YearLevelID) AS LevelID FROM LevelsAttained GROUP BY StudentID) g0 
ON g0.StudentID = s.StudentID 
JOIN YearLevels ON g0.LevelID = l.YearLevelID 

Answer 3

你可以使用一个公共表表达式与ROW_NUMBER窗函数：

WITH CTE AS(
    SELECT RN = 
     ROW_NUMBER()OVER(PARTITION BY la.StudentID ORDER BY la.YearLevelID DESC) 
    , FirstName + ' ' + LastName AS FullName 
    , YearLevelName 
    FROM Students s 
    INNER JOIN LevelsAttained la ON s.StudentID = la.StudentID 
    INNER JOIN YearLevels yl ON la.YearLevelID = yl.YearLevelID 
) 
SELECT FullName, YearLevelName FROM CTE WHERE RN = 1 

Answer 4

select s.firstname + ' ' + s.lastname, y.yearlevelname from 
students s 
inner join (select max(yearlevelid) yearlevelid, studentid from levelsattained group by studentid) l on s.studentid = l.studentid 
inner join YearLevels y on l.yearlevelid = y.yearlevelid