Question

department(dept_name, building, budget)

course(course_id, title, dept_name, credits)

instructor(ID, name, dept_name, salary)

section(course_id, sec_id, semester, year, building, room_number, time_slot_id)

teaches(ID, course_id, sec_id, semester, year)

student(ID, name, dept_name, tot_cred)

takes(ID, course_id, sec_id, semester, year, grade)

查找超过50名学生参加的每门课程的课程名称，学期和年份

select course.title , takes.semester , takes.year
from course
natural join takes
where course.course_id = takes.course_id
having count(distinct ID) > 50

查找包含多个部分的每门课程的标题

select title 
from course
natural join section 
where course.course_id = section.course_id
having count(distinct sec_id) > 1

查找在Comp中教授5门以上课程的所有教师的ID。科学。系

select ID
from instructor
natural join course
where course.dept_name = instructor. dept_name
having count(credits)>5

这也应该是学分或course_id

查找未教授生物系提供的任何模块的所有教师

这个我甚至没有从哪里开始

Answer 1

您的所有查询都缺少GROUP BY条款。

如果您使用NATURAL JOIN，则不需要WHERE子句来关联表格 - NATURAL JOIN会自动执行此操作。

select course.title , takes.semester , takes.year
from course
natural join takes
GROUP BY course.title, takes.semester, takes.year    
having count(distinct ID) > 50

select title 
from course
natural join section 
GROUP BY title
having count(distinct sec_id) > 1

select ID
from instructor
natural join course
GROUP BY ID
having count(credits)>5

您的上一个查询还有其他一些问题。您没有使用teaches表格将教师链接到课程，也不会检查课程是否在Comp中。科学。部。

SELECT i.id
FROM instructor AS i
JOIN teaches AS t ON i.id = t.sec_id
JOIN course AS c ON t.course_id = c.id
WHERE c.dept_name = "Comp. Sci."
HAVING COUNT(*) > 5

Answer 2

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不确定我正确地进行sql查询

2 个答案: