SQL Server：从两个表中选择，默认值为0

Question

表格 - BASECASE（CaseNumber，PatientID）

CaseNumber------PatientID
S100---------------P201
S101---------------P201
S102---------------P200
S103---------------P199
S104---------------P201

第二桌

Table - CHECKUP(CheckupNumber, CaseNumber)
CheckupNumber------CaseNumber
C301-------------------S100
C302-------------------S100
C303-------------------S101
C304-------------------S102
C305-------------------S103

SQL代码

SELECT CaseNumber FROM BASECASE
 & COUNT(CaseNumber)FROM CHECKUP, WHERE PatientID='P201'

如果CHECKUP中不存在CaseNumber，则COUNT（CaseNumber）[将为null]应返回值0.

预期结果。

CaseNumber-----No.Of Checkups
S100------------------2
S101------------------1
S104------------------0

如何解决这个问题？

Answer 1

您需要使用left join和group by

select B.caseNumber, ISNULL(count(C.checkupNumber) ,0)
from BaseTable B
left join Checkup C
on B.caseNumber = C.caseNumber
where B.patientId ='P201'
group by B.caseNumber

Answer 2

加入Group BY

select BC.Casenumber,isnull(COUNT(BC.Casenumber),0) CNT from BaseCase BC
left
join CheckUp Ch
on BC.CasetNumber=Ch.CaseNumber
group by BC.Casenumber

Answer 3

您需要使用左加入与分组

SELECT cn.cno，Count（cp.cno）as NoCheckup from casenumber cn LEFT JOIN checkup cp ON cn.cno = cp.cno                      WHERE cn.patientid ='P201'                      GROUP BY cn.cno