Question

我在执行这一个SQL作业问题时遇到了一些麻烦，并尝试了多次不同的尝试，但仍然得到了同样错误的答案。我不确定我错过了什么，如果有人能帮助我，那真的很棒！：）

问题：显示在同一学期至少教授2门课程的所有教授的不同身份

以下是给我们的表格：

DROP TABLE IF EXISTS PROFESSOR;  
CREATE TABLE PROFESSOR (  
    Id   VARCHAR (9),   
    Name    VARCHAR (32),  
    DepartmentId  VARCHAR (3),   
    PRIMARY KEY (Id),  
    FOREIGN KEY (DepartmentId) REFERENCES DEPARTMENT (Id)  
)ENGINE=INNODB;

INSERT INTO PROFESSOR VALUES  
('P01', 'Rao',      'CSC'),  
('P02', 'Mitra',    'CSC'),  
('P03', 'Smith',    'MTH'),  
('P04', 'Miller',   'MTH'),  
('P05', 'Abwender', 'PSH'),  
('P06', 'Speed',    'PSH');  

DROP TABLE IF EXISTS TEACHING_ASSIGNMENT;  
CREATE TABLE TEACHING_ASSIGNMENT (  
    ProfessorId VARCHAR (9), -- Department Code may be different   
    CourseCode  VARCHAR (6), -- This is like CIS422  
    Semester    VARCHAR (16),-- This is like Fall 2016  
    Section     VARCHAR (3), -- This is like 01  
    PRIMARY KEY (ProfessorId, CourseCode, Semester, Section),  
    FOREIGN KEY (ProfessorId) REFERENCES PROFESSOR (Id),  
    FOREIGN KEY (CourseCode)  REFERENCES COURSE (CourseCode)  
)ENGINE=INNODB;  


INSERT INTO TEACHING_ASSIGNMENT VALUES  
('P01', 'CSC203', 'Fall 2015', '01'),  
('P02', 'CIS202', 'Fall 2015', '01'),  
('P03', 'MTH201', 'Fall 2015', '01'),  
('P04', 'MTH281', 'Fall 2015', '01'),  
('P05', 'PSH110', 'Fall 2015', '01'),  
('P06', 'PSH201', 'Fall 2015', '01'),  
('P01', 'CIS202', 'Fall 2015', '02'),  
('P03', 'CSC203', 'Spring 2016', '01'),  
('P02', 'CIS202', 'Spring 2016', '01'),  
('P03', 'MTH201', 'Spring 2016', '01'),  
('P04', 'MTH281', 'Spring 2016', '01'),  
('P05', 'PSH110', 'Spring 2016', '01'),  
('P06', 'PSH201', 'Spring 2016', '01'),  
('P01', 'CIS202', 'Spring 2016', '02');

我的SQL：

SELECT DISTINCT Id
FROM PROFESSOR
WHERE Id IN
    (SELECT ProfessorId
     FROM TEACHING_ASSIGNMENT
     GROUP BY Semester
     HAVING COUNT() >= 2);

我得到的答案：P01

但正确的答案应该是P01和P03。

Answer 1

不需要子查询：

@protocol Class1<NSObject>

- (void)searchBy:(Enum1)searchType;

@end

Answer 2

GROUP BY应该包含ProfessorId，因为您正在计算一个学期教授讲授的课程数量。试试这个：

SELECT DISTINCT Id
FROM PROFESSOR
WHERE Id IN
    (SELECT ProfessorId
     FROM TEACHING_ASSIGNMENT
     GROUP BY Semester, ProfessorId
     HAVING COUNT(*) >= 2);

Answer 3

下面是查询，我在创建新表后检查了它。

select Courses.ProfessorId, count(*) from Cou_Pro Courses 
group by Courses.ProfessorId, Courses.Semester having
count(Courses.ProfessorId) > 1

展示在同一学期至少教授2门课程的所有教授的独特身份

3 个答案: