sql - 如何计算一对多的关系

Question

ReporterTbl与 AttachmentTbl 有一对多的关系.

在 ReporterTbl , 我有一个 ID (101) 并且我可以有 AttachmentTbl不止一个Attachment与 ReporterTbl.Id 相关

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 ，多少 Attachment我有吗？

表结构:

 ReporterTbl

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

    AttachmentTbl:

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

Answer 1

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