我想知道我是否可以获得一些关于我所做的关系代数的反馈以及任何关于改进它的建议,如果您发现我的 SQL 有任何问题,您能否指出它。
SELECT CourseName
FROM Course
WHERE CourseNo = 6;
∏CourseName(σCourseNo=6(Course))
SELECT CU.UnitNo
FROM C.Course, CU CourseUnit
WHERE C.CourseName = CU.CourseNo
AND C.CourseName = 'Research';
∏UnitNo(CourseUnit(σCourseName='研究'(Course)))
SELECT U.UnitName
FROM S Student, SU StudentUnit, U Unit
WHERE S.StudentNo = SU.StudentNo
AND SU.UnitNo = U.UnitNo
AND S.StudentName = 'John Perry';
∏UnitName(Unit(StudentUnit(σStudentName='John Perry'(Student))))
SELECT count(S.StudentNo) ResearchStudents
FROM C Course, S Student
WHERE C.CourseNo = S.CourseNo
AND C.CourseName = 'Research';
∏ResearchStudents((C)count(StudentNo)(学生(σCourseName='Research'(Course))))