sql - Relational Algebra -

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I was wondering if I could get some feedback on relational algebra and if you are looking, Any advice on anything with my SQL may be wrong, you can get it out. 

  Select course course where course no.6 =;

ΠCourseName (σCourseNo = 6 (Course)) 

  CU Choose. C. There is no unit with sys, cu course WHERE C.CourseName = CU.CourseNo and C.CourseName = 'research';

ΠUnitNo (Course Unit (σCourseName = 'Research' (Course)) 

  Select from U.UnitName Student SU StudioUinet, U unit where S. student no .: SU.StudentNo and SU.UnitNo = U.UnitNo and S.StudentName = 'John Perry';

ΠUnitName (Student Unit (Student Unit (σStudentName = 'John Perry' (student))) 

  SELECT count (S. student no) association student from C course Course New = S. Course and N.

ΠResearchStudents ((C) Count (not Student) (Student (ΣCourseName = 'research' (course))

There is a problem with the section, I removed a dot between C. Course 

  SELECT CU from the syllabus, the CU course unit where C. Course name = CU course no and C. course name = 'Research ';

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