Question

目前我有两张桌子，约会和用户：

appointment_id | time | teacher_id | student_id
1              |  11  |     2      |     1
2              |  12  |     2      |     1

user_id |  name
1       | student
2       | teacher

期望的结果：

appointment_id | time | teachername | studentname
1              |  11  |   teacher   |    student
2              |  12  |   teacher   |    student

基本上我想从约会表中做一个SELECT *，但是不是给我ID的查询，我希望名字替换它们。我尝试过创建一个临时表和一个JOIN，但无法弄明白。任何帮助都会很棒，谢谢！

Answer 1

这个怎么样？

SELECT
    appointment_id,
    time,
    u.name AS teachername,
    v.name AS studentname
FROM
    appointments AS a
LEFT JOIN
    users AS u ON
    a.teacher_id = u.user_id
LEFT JOIN
    users AS v ON
    a.student_id = v.user_id

您可以查看 SQL Fiddle

Answer 2

试试这个

   select a.appointment_id , a.time ,b.name as teachername ,
          c.name as studentname
   from appointments a 
   inner join users b
   on a.teacher_id = b.user_id
   inner join users c
   on a.student_id = c.user_id

DEMO HERE

输出：

   APPOINTMENT_ID   TIME    TEACHERNAME     STUDENTNAME
          1          11     teacher         student
          2          12     teacher         student

从另一个表中使用值替换列时，从表中选择所有数据？

2 个答案: