您值得收藏的关系代数与Sql练习网站及实战操作

instructor(ID, name, dept_name, salary)
deptment(dept_name, building, budget)
student(ID, name, dept_name, tot_cred)
course(course_id, title, dept_name, credts)
takes(ID, course_id, semester, year, grade)

教师信息instructor：教师号ID，教师名字name，教师所在的系dept_name，薪资salary
建筑department：系名dept_name, 建筑building, 预算budget
学生信息student：学生学号ID，学生姓名name，学生所在系dept_name，总学分tot_cred
课程course：课程号course_id，课程名称title，课程所属的系名dept_name，学分credits
选课信息takes：学生学号ID，课程标识course_id，课程段标识sec_id，学期semester，年份year，成绩grade

select distinct name from instructor;

π name (instructor)

select distinct name from student;

π name (student)

select b.building from instructor as a, department as b where a.name='Kim' and a.dept_name=b.dept_name;

π b.building (σ a.name = 'Kim' and a.dept_name = b.dept_name ((ρ a instructor) ⨯ (ρ b department)))

select tot_cred from student where dept_name='Comp. Sci.';

π ID, name, tot_cred σ dept_name = 'Comp. Sci.' (student)

select s.*,t.grade from student as s,course as c,takes as t where s.dept_name=c.dept_name and t.course_id=c.course_id and c.title='Database System Concepts' and t.grade='A';

π s.ID,s.name,s.dept_name,s.tot_cred σ c.title='Database System Concepts' and t.grade='A' and c.dept_name=s.dept_name and c.course_id=t.course_id (ρ c course ⨯ ρ t takes ⨯ ρ s student)

π b.ID,b.name,b.dept_name,b.tot_cred σ a.ID=b.ID ((ρ a ((π ID student) - (π ID takes))) ⨯ (ρ b (student)))