MySQL连接表Q

Question

我有3张桌子，一个叫Doctor，Person，另一个叫Appointment。他们有共同的关系doctor_id，但只有人持有他们的Last_Name。

我需要能够生成一个医生ID的列表，以及为每个有零个或多个约会的医生所做的约会数量以及医生姓名。

我该如何实施医生的名字？

下面是表

http://i.stack.imgur.com/Vx3x9.png

这是我迄今为止

SELECT doctor.doctor_id, COUNT(appt_time) AS No_APP 
FROM doctor LEFT JOIN appointment ON doctor.doctor_id = appointment.doctor_id 
GROUP BY doctor.doctor_id; 

Answer 1

只需添加一个左边加入新表：

SELECT doctor.doctor_id, COUNT(appt_time) AS No_APP, person.Last_name 
FROM doctor LEFT JOIN appointment ON doctor.doctor_id = appointment.doctor_id 
      LEFT JOIN person on person.doctor_id = doctor.doctor_id 
GROUP BY doctor.doctor_id; 

Answer 2

假设人表中包含一个链接，医生

SELECT d.doctor_id, p.last_name, COUNT(a.appt_time) AS No_APP 
FROM doctor d 
LEFT JOIN appointment a ON d.doctor_id = a.doctor_id 
LEFT JOIN person p ON d.doctor_id = p.doctor_id 
GROUP BY d.doctor_id;