SQL Server查看从相关表中获取计数where column =“True”

Question

我在SQL Server中有一对一关系（申请人，参考）中的两个相关表。

我想要一个视图，它将从Applicant表中检索所有数据，并向视图中添加另一列，告诉我有多少相关的引用行存在“完成”列为True的位置。

Answer 1

像这样使用子查询：

select applicantfield1, applicantfield2, 
    (select count(*) from 
    reference where reference.applicantkey = applicant.applicantkey 
    and reference.complete = 1) AS referencecount 
from applicant 

除非完整场是在本申请人表（未参考表）。如果是这样，它会更像是这样的：

select applicantfield1, applicantfield2, 
    (select count(*) from 
    reference where 
    reference.applicantkey = applicant.applicantkey) AS referencecount 
from applicant 
where applicant.complete = 1 

Answer 2

像下面这样。你需要加入一张桌子。这将处理申请人还没有真实参考的地方。

SELECT A.*, isnull(r.comptotal,0) as CompleteTotal 
FROM Applicant as a Left Join 
    (SELECT ApplicantId, Count(Complete) as comptotal 
    FROM Reference Where Complete=1 Group by ApplicantID) as r 
    on a.ApplicantId = r.applicantId