使用Sql查詢的全外部聯接

我有一個Sql查詢的問題。因此，我的第一份工作表的結構：使用Sql查詢的全外部聯接

表結構 - StudentGrade

ID - Department - StudentID - Grade - Course 
-------------------------------------------- 
1  2   2002  A+  102 
2  2   2002  B+  102 
3  2   2002  A+  104

我應該得到的輸出如下：

ID - Department - StudentID - Grade - Course 
---------------------------------------------- 
2  2   2002  B+  102 // as this was inserted last 
3  2   2002  A+  104

我利用所獲得的上述結果以下查詢只有在存儲在StudentGrade表中的結果存在時才能正常工作：

SELECT 
    COALESCE(m.Grade, 'Not Graded Yet') AS Grade 
FROM 
    StudentGrade m 
FULL OUTER JOIN 
    EnrollCourse k ON k.Course = m.Course 
WHERE 
    m.ID IN (SELECT MAX(m.ID) 
      FROM StudentGrade m 
      GROUP BY m.StudentID, m.Course) 
    AND m.StudentID = 2002 // this query returns the grade that is inserted lastly for a course and for a specific student

順便說一句，爲EnrollCourse表結構如下：

ID - StudentID - Course - EnrollDate 
------------------------------------- 
1  2002  102 NULL 
2  2002  104 NULL

的結果是合格的在校生我的意思是在一門課程註冊學生。所以現在我的要求是，假設StudentID 2002被註冊了兩門課程。如果無級分配給學生，然後輸出我從StudentGrade表期待：

ID - Department - StudentID - Grade -   Course 
------------------------------------------------------ 
1  2   2002  No Grade Yet  102 
2  2   2002  No Grade Yet  104

如果分配的過程102，那麼這將是如下：

ID - Department - StudentID - Grade -  Course 
--------------------------------------------------- 
1  2   2002  B+    102 
2  2   2002  No Grade Yet 104

同樣，如果課程成績就像是A +更新，那麼這將是：

ID - Department - StudentID - Grade -   Course 
------------------------------------------------------ 
1  2   2002  A+     102 
2  2   2002  No Grade Yet  104

有查詢一些INNER JOIN。所以我試圖用下面（只是修改了上面，這似乎是不工作）：

SELECT 
    COALESCE(m.Grade, 'Not Graded Yet') AS Grade 
FROM 
    StudentGrade m 
FULL OUTER JOIN 
    EnrollCourse k ON k.Course = m.Course 
WHERE 
    m.ID IN (SELECT MAX(m.ID) 
      FROM StudentGrade m 
      FULL OUTER JOIN EnrollCourse k ON k.Course = m.Course 
      GROUP BY m.StudentRegNo, m.Course) 
    AND m.StudentID = 2002

來源

2016-08-15 AT-2017

當FULL OUTER JOIN，移動從哪裏開來獲得真正的外部表的條件聯接結果。（現在m是「內連接」。）在你的情況下，用AND替換WHERE。 – jarlh

首先你要麼需要系EnrollCourse或者您需要一個表來處鏈接到課程。在我的例子，我採取了簡單的方法，並添加系EnrollCourse

DECLARE @enrollCourse TABLE (
ID int, 
StudentID int, 
Course int, 
Department int 
) 

DECLARE @studentGrade TABLE (
ID int, 
Department int, 
StudentID int, 
Grade varchar(2), 
Course int 
) 

INSERT INTO @enrollCourse VALUES (1, 2002, 102, 2) 
INSERT INTO @enrollCourse VALUES (2, 2002, 104, 2) 

SELECT ec.ID, ec.Department, ec.StudentID, COALESCE(sG.Grade, 'Not Graded Yet') as Grade, eC.Course FROM @enrollCourse eC left join 
(SELECT ID, Department, StudentID, Grade, Course FROM @studentGrade s INNER JOIN (SELECT MAX(ID) as MaxID FROM @studentGrade GROUP BY Department, StudentID, Course) mG ON s.ID = mG.MaxID) sG ON 
ec.StudentID = sG.StudentID and ec.Course = sg.Course and ec.Department = sg.Department 

INSERT INTO @studentGrade VALUES(1, 2, 2002, 'B+', 102) 

SELECT ec.ID, ec.Department, ec.StudentID, COALESCE(sG.Grade, 'Not Graded Yet') as Grade, eC.Course FROM @enrollCourse eC left join 
(SELECT ID, Department, StudentID, Grade, Course FROM @studentGrade s INNER JOIN (SELECT MAX(ID) as MaxID FROM @studentGrade GROUP BY Department, StudentID, Course) mG ON s.ID = mG.MaxID) sG ON 
ec.StudentID = sG.StudentID and ec.Course = sg.Course and ec.Department = sg.Department 

DELETE FROM @studentGrade 

INSERT INTO @studentGrade VALUES(1, 2, 2002, 'A+', 104) 

SELECT ec.ID, ec.Department, ec.StudentID, COALESCE(sG.Grade, 'Not Graded Yet') as Grade, eC.Course FROM @enrollCourse eC left join 
(SELECT ID, Department, StudentID, Grade, Course FROM @studentGrade s INNER JOIN (SELECT MAX(ID) as MaxID FROM @studentGrade GROUP BY Department, StudentID, Course) mG ON s.ID = mG.MaxID) sG ON 
ec.StudentID = sG.StudentID and ec.Course = sg.Course and ec.Department = sg.Department 

INSERT INTO @studentGrade VALUES(2, 2, 2002, 'B+', 102) 

SELECT ec.ID, ec.Department, ec.StudentID, COALESCE(sG.Grade, 'Not Graded Yet') as Grade, eC.Course FROM @enrollCourse eC left join 
(SELECT ID, Department, StudentID, Grade, Course FROM @studentGrade s INNER JOIN (SELECT MAX(ID) as MaxID FROM @studentGrade GROUP BY Department, StudentID, Course) mG ON s.ID = mG.MaxID) sG ON 
ec.StudentID = sG.StudentID and ec.Course = sg.Course and ec.Department = sg.Department 

INSERT INTO @studentGrade VALUES(3, 2, 2002, 'B+', 104) 

SELECT ec.ID, ec.Department, ec.StudentID, COALESCE(sG.Grade, 'Not Graded Yet') as Grade, eC.Course FROM @enrollCourse eC left join 
(SELECT ID, Department, StudentID, Grade, Course FROM @studentGrade s INNER JOIN (SELECT MAX(ID) as MaxID FROM @studentGrade GROUP BY Department, StudentID, Course) mG ON s.ID = mG.MaxID) sG ON 
ec.StudentID = sG.StudentID and ec.Course = sg.Course and ec.Department = sg.Department

來源

2016-08-15 06:02:14

非常感謝。它像一個魅力。 –

使用Sql查詢的全外部聯接

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