sql – 如何计算一对多关系

ReporterTbl与AttachmentTbl有一对多的关系.

在ReporterTbl中,我有一个ID(101),我可以使用AttachmentTbl多个与ReporterTbl.Id相关的附件

SELECT     
ISNULL(ReporterTbl.Id,0) AS Id,CONVERT(char(10),ReporterTbl.StartDate,101) AS StartDate,ISNULL(ReporterTbl.PriorityId,0) AS PriorityId,ISNULL(dbo.ReporterTbl.PriorityDesc,'') AS PriorityDesc,(select       
   ReporterTbl.Id,COUNT(dbo.AttachmentTbl.Id) AS attachment_Id
FROM         
dbo.AttachmentTbl RIGHT OUTER JOIN
ReporterTbl ON dbo.AttachmentTbl.Id = ReporterTbl.Id
GROUP BY ReporterTbl.Id) AS IsAttachment
)

基本上,我想知道的是ReporterTbl.ID,我有多少个附件？

表结构：

ReporterTbl

    Id int   {**PrimaryKey**}
    StartDate datetime
    PriorityId int
    PriorityDesc varchar(500

    AttachmentTbl:

    AttachmentId indentity
    Id {**FK to ReproterTbl**}
    Filename
    Content
    ...

解决方法

select r.id,count(a.id) as Count
from ReporterTbl r
left outer join AttachmentTbl a on r.id = a.id
group by r.id

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