SQL Server - 一个查询结果中的多个计数问题

Question

我正在尝试使用 SELECT 查询计算学生的成绩。这基于 3 个表格：

• 学生（StudentID 主键）
• 等级（GradeID 主键）
• GradeLine（GradeLineID 主键、StudentID 外键、GradeID 外键）

问题：使用以下查询时，如果条件之一为空（例如 Student 3 没有区别，但在所有其他列中都有标记），则从查询中删除 Student ，我希望它们仍然存在并且只显示一个 0

SELECT
    GradeLine.StudentID,
    COUNT(CASE WHEN GradeLine.GradeID = 1 THEN (GradeLine.GradeID) END) AS Distinction,
    COUNT(CASE WHEN GradeLine.GradeID = 2 THEN (GradeLine.GradeID) END) AS  Merit,
    COUNT(CASE WHEN GradeLine.GradeID = 3 THEN (GradeLine.GradeID) END) AS Pass,
    COUNT(CASE WHEN GradeLine.GradeID = 4 THEN (GradeLine.GradeID) END) AS Fail,
    COUNT (GradeLine.GradeID) AS Total
FROM 
    GradeLine
GROUP BY 
    GradeLine.StudentID

预期数据示例：

StudentID   Distinction Merit   Pass    Fail    Total
------------------------------------------------------
   1             1         3     4       2       10
   2             1         7     2       1       11
   3             0         3     3       5       11
   4             0        12     0       0       12
   5             6         3     0       0        9

请有人告诉我我做错了什么？

新的当前结果：

StudentID   Distinction Merit   Pass    Fail    Total
-----------------------------------------------------
   1             0        0      10      0       10
   2            11        0       0      0       11
   3             0        0       0     11       11
   4             0       12       0      0       12
   5             0        0       0      9        9

表格代码、约束和示例数据：

--CREATE TABLES
CREATE TABLE Student (StudentID INT IDENTITY (1,1) NOT NULL,
Studentname VARCHAR(50))

CREATE TABLE Grade (GradeID INT IDENTITY (1,1) NOT NULL,
Gradename VARCHAR(50))

CREATE TABLE GradeLine (GradeLineID INT IDENTITY (1,1) NOT NULL,
StudentID INT,
GradeID INT)

--PK CONSTRAINTS
ALTER TABLE Student ADD CONSTRAINT StudentID_PK PRIMARY KEY (StudentID)
ALTER TABLE Grade ADD CONSTRAINT GradeID_PK PRIMARY KEY (GradeID)
ALTER TABLE GradeLine ADD CONSTRAINT GradeLine_PK PRIMARY KEY (GradeLineID)

--FK CONSTRAINTS
ALTER TABLE GradeLine ADD CONSTRAINT StudentID_GL2S FOREIGN KEY (StudentID) REFERENCES Student (StudentID)
ALTER TABLE GradeLine ADD CONSTRAINT GradeID_GL2G FOREIGN KEY (GradeID) REFERENCES Grade (GradeID)

--DATA 
INSERT INTO Student VALUES ('Student A')
INSERT INTO Student VALUES ('Student B')
INSERT INTO Student VALUES ('Student C')

INSERT INTO Grade VALUES ('Distinction')
INSERT INTO Grade VALUES ('Merit')
INSERT INTO Grade VALUES ('Pass')
INSERT INTO Grade VALUES ('Fail')

--STUDENT A 
INSERT INTO GradeLine VALUES (1, 1) --STUDENT A DISTINCTION
INSERT INTO GradeLine VALUES (1, 1) --STUDENT A DISTINCTION
INSERT INTO GradeLine VALUES (1, 2) --STUDENT A MERIT

--STUDENT B
INSERT INTO GradeLine VALUES (2, 1) --STUDENT A DISTINCTION
INSERT INTO GradeLine VALUES (2, 1) --STUDENT A DISTINCTION
INSERT INTO GradeLine VALUES (2, 2) --STUDENT A MERIT
INSERT INTO GradeLine VALUES (2, 5) --STUDENT A FAIL

--STUDENT C
INSERT INTO GradeLine VALUES (3, 2) --STUDENT A MERIT
INSERT INTO GradeLine VALUES (3, 3) --STUDENT A PASS
INSERT INTO GradeLine VALUES (3, 4) --STUDENT A FAIL

Answer 1

您可以使用PIVOT：

SELECT      piv.StudentID,
            piv.[1] AS Distinction,
            piv.[2] AS Merit,
            piv.[3] AS Pass,
            piv.[4] AS Fail,
            (piv.[1] + piv.[2] + piv.[3] + piv.[4]) AS Total
FROM 
(
  SELECT    StudentID, GradeID
  FROM      GradeLine
) src
PIVOT
(
  COUNT(GradeID)
  FOR GradeID IN ([1], [2], [3], [4])
) piv;

这应该在COUNT 为 0 的情况下开箱即用。

您可以在这里查看整个操作 -> http://rextester.com/NUER1494

希望对你有帮助！！！