如何选择哪个医生没有看病人？

Question

在我的表格中，每位医生都有患者。我尝试使用大小写来完成此操作，但是它不起作用。

SELECT DoctorID
    CASE 
    WHEN  COUNT(DISTINCT PatientID) = 0 THEN 'There is no doctor who hasn't admitted any patients. '
    ELSE 'There is no doctor who hasn't admitted any patients.
FROM Visits
GROUP BY DoctorID; 

Answer 1

我认为您想要not exists。如果医生没有看病人，那么我就不会期望那个医生出现在visits表中。因此：

select d.*
from doctors d
where not exists (select 1 from visits v where v.doctorid = d.doctorid);

Answer 2

下面会工作吗？

SELECT DoctorID, count(DISTINCT PatientID) 
FROM VISITS
GROUP BY DoctorID
HAVING COUNT(DISTINCT PatientID) = 0