如何统计没有患者预约的医生？

Question

结果如下：

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还是其他什么？像：

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

Answer 1

你可以不使用（在这种情况下没有区别）

无病人的医生数量

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

医生的身份

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

Answer 2

使用以下查询

   SELECT * from `Doctors`
    WHERE `DoctorID` NOT IN (SELECT DISTINCT(`doctorID`) FROM `bookings`);