mysql - SQL select from inner join where count 大于

Question

医生

doctorid (PK)
doctorname

Patient

patientid (PK)
patientname
doctorid

I have the following query to get the doctors details with the number of patients that he/she consults. assume a patient has only one doctor to consult.

select d.doctorid,d.doctorname,count(p.patientid)
from doctor d
inner join patient p
on d.doctorid = p.doctorid
group by p.doctorid

现在我需要获取相同的信息，但仅限于拥有超过 1 个患者的医生。请给我一个查询建议。

Answer 1

使用HAVING clause

SELECT d.doctorid,
       d.doctorname,
       COUNT(p.patientid) AS patients
  FROM doctor d
       INNER JOIN patient p
                  ON d.doctorid = p.doctorid
GROUP BY 
       d.doctorid,
       d.doctorname
HAVING patients > 1

我使用别名 (patients) 而不是 COUNT(p.patientid)，因为 HAVING 子句允许这样做。但您也可以坚持使用 COUNT(p.patientid)
另外，我建议您在 GROUP BY 子句中使用所有非聚合列。
而且，如果您检索 doctorname，您可能不必检索 doctorid。