SQL 顯示GROUP BY中的最新記錄？

Question

我有一個看起來像這樣的表：

id    |    SubjectCode    |    Grade    |    DateApproved    |    StudentId

1            SUB123            1.25            1/4/2012            2012-12345

2            SUB123            2.00            1/5/2012            2012-12345

3            SUB123            3.00            1/5/2012            2012-98765   

我正在嘗試 GROUP BY SubjectCode 但我希望它顯示最新的 DateApproved 所以它看起來像：

  id    |    SubjectCode    |    Grade    |    DateApproved    |    StudentId

2            SUB123            2.00            1/5/2012            2012-12345

3            SUB123            3.00            1/5/2012            2012-98765  

我對如何去做有點迷茫？

編輯：

好的，伙計們，我現在在我的真實電腦上，對於構建不當的問題感到抱歉。

這是我實際上想做的事情：

SELECT GD.GradebookDetailId, G.SubjectCode, G.Description, G.UnitsAcademic, G.UnitsNonAcademic, 
GD.Grade, GD.Remarks, G.FacultyName, STR_TO_DATE(G.DateApproved, '%m/%d/%Y %h:%i:%s') AS 'DateAproved'
FROM gradebookdetail GD INNER JOIN gradebook G ON GD.GradebookId=G.GradebookId 
WHERE G.DateApproved IS NOT NULL AND G.GradebookType='final' AND StudentIdNumber='2012-12345'

GROUP BY <?????>
ORDER BY G.SubjectCode ASC

基本上，我只想顯示“SubjectCode”的最新“DateApprove”，所以我不會獲得多個條目。

Answer 1

從這個開始：

select StudentId, max(DateApproved) 
from tbl
group by StudentId

然后將其集成到主查詢：

select * 
from tbl
where (StudentId, DateApproved) in

(
  select StudentId, max(DateApproved) 
  from tbl
  group by StudentId
)

你也可以使用這個：

select * 
from tbl
join (select StudentId, max(DateApproved) as DateApproved 
      from tbl 
      group by StudentId)
using (StudentId, DateApproved)

但我更喜歡元組測試，它更整潔

現場測試： http ://www.sqlfiddle.com/#!2/771b8/5

Answer 2

SELECT t2.*
FROM temp t2 
INNER JOIN(
    SELECT MAX(DateApproved) as MaxDate, StudentId
    FROM temp
    GROUP BY StudentId
    ) t1 ON t1.MaxDate = t2.DateApproved and t1.StudentId = t2.StudentId

Answer 3

對於在撰寫本文時（2020 年）仍不支持元組的 SQL Server 中嘗試此操作的用戶，您可以使用以下內容（在此處改進另一個答案）

改變這個：

-- MYSQL
select * 
from tbl
where (StudentId, DateApproved) in
(
  select StudentId, max(DateApproved) 
  from tbl
  group by StudentId
)

進入這個：

-- Microsoft SQL Server
select * 
from tbl
where concat(StudentId, DateApproved) in
(
  select concat(StudentId, max(DateApproved)) 
  from tbl
  group by StudentId
)

Answer 4

SELECT *
FROM TheTable a
WHERE NOT EXISTS(SELECT *
                 FROM TheTable b
                 WHERE b.StudentCode = a.StudentCode AND b.DateApproved > a.DateApproved)

Answer 5

這對我在 postgres 中更有效。

select * from tbl t1 where t1.DateApproved = (select max(t2.DateApproved) from tbl t2 where t2.StudentId = t1.StudentId)

Answer 6

此代碼適用於 SQL Server 2016。

select StudentId, max(DateApproved) 來自 tbl group by StudentId

此代碼將顯示每個學生 ID 批准的最大和最小日期。

select StudentId，最大值（批准日期），最小值（批准日期）
來自 tbl 按 StudentId 分組