从表中选择一个字段具有相同值的行
问题描述：
我有一个带有以下两个表的MySQL数据库:
I have a MySQL database with these two tables:
Tutor(tutorId, initials, lastName, email, phone, office)
Student(studentId, initials, lastName, email, tutorId)
要查询共享同一位导师的任何学生的姓名缩写和姓氏是什么?
What is the query to return the initials and last names of any student who share the same tutor?
我尝试了SELECT intials, lastName FROM Student WHERE tutorId = tutorId，但这只是返回所有学生的姓名.
I tried SELECT intials, lastName FROM Student WHERE tutorId = tutorId but that just returns the names of all students.
答
您将不得不与学生对抗:
You'll have to join students against itself:
SELECT s1.initials, s1.lastName
FROM Student s1, Student s2
WHERE s1.studentId <> s2.studentID /* Every student has the same tutor as himself */
AND s1.tutorId = s2.tutorid
如果要输出对:
SELECT s1.initials, s1.lastName, s2.initials, s2.lastName
FROM Student s1, Student s2
WHERE s1.studentId <> s2.studentID /* Every student has the same tutor as himself */
AND s1.tutorId = s2.tutorid
要获取教师列表-学生:
To get a list of Tutor - Students:
SELECT tutorId, GROUP_CONCAT( initials, lastName SEPARATOR ', ')
FROM `Student`
GROUP BY tutorId
/* to only show tutors that have more than 1 student: */
/* HAVING COUNT(studentid) > 1 */