php - 如何统计没有患者预约的医生？

Question

这个问题已经有答案了:

How to count how many doctors are booked by each patient? (4 个答案)

已关闭 7 年前。

结果应如下所示:

Doctors_have_no_patients
Doctor2
Doctor3
Doctor5

表格

Doctor table called `Doctors`
**DoctorID**
Doctor1
Doctor2
Doctor3
Doctor4
Doctor5


Booking table called `Bookings`

PatientID  DoctorID  Date
Patient1   Doctor1   etc.
Patient2   Doctor4   etc.
Patient3   Doctor1   etc.

我应该使用 distinct或者其他的东西？喜欢:

select Bookings.DoctorID as Doctors_have_no_patients count(distinct(Bookings.PatientID))...

Answer 1

您可以使用 not in (在本例中也可以使用 not unique)

没有病人的医生数量

select count(*) from Doctors
where DoctorId not in (select doctorID from bookings);

医生ID

select DoctorID from Doctors
where DoctorId not in ( select doctorID from bookings);