[英]SQL query, multiple JOIN and SELECT (?) statements
我查看了很多答案,并在代码中尝试了不同的选项,但我无法得到我需要的结果或者查询根本不起作用。 所以不得不求助。
这是学校实验室的任务,但我这周病了,所以错过了问老师的机会,现在这个和更多类似任务的截止日期是这个周末,所以必须以某种方式弄清楚
我需要合并三个表。 没问题,但是从同一个表(教师)中,我需要获得每门课程的教师姓名以及课程的顾问教师(来自主题)。
这两个查询单独工作,但我无法弄清楚将它们合二为一的方法。
--displays all courses (its number, implementation, name) and teachers on the course
SELECT Course.subjectnumb, Course.coursenumb, Subject.subjectname, Course.participants, Teacher.firstname, Teacher.surname
FROM Course JOIN Subject on Course.subjectnumb = Subject.subjectnumb
JOIN Teacher on Course.teachernumb = Teacher.teachernumb
ORDER BY Subject.subjectname ASC, Course.coursenumb ASC, Teacher.surname ASC
--display advisors names
SELECT teacher.firstname, teacher.surname
FROM subject JOIN teacher ON teacher.teachernumb = subject.advisor
ORDER BY teacher.surname ASC, teacher.firstname ASC
您可以在同一张桌子上加入两次。 例如 :
SELECT C.subjectnumb, C.coursenumb,
S.subjectname, C.participants,
TC.firstname as course_teacher_firstname, TC.surname as course_teacher_surname,
TS.firstname as subject_advisor_firstname, TS.surname as subject_advisor_surname,
FROM Course C JOIN Subject S on C.subjectnumb = S.subjectnumb
JOIN Teacher TC on C.teachernumb = TC.teachernumb
JOIN Teacher TS on S.advisor = TS.teachernumb
ORDER BY S.subjectname ASC, C.coursenumb ASC, TC.surname ASC
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