如何計算一對多的關係

ReporterTbl有一個與AttachmentTbl一對多的關係。如何計算一對多的關係

在ReporterTbl，我有一個ID（101），我可以有ReporterTbl.Id

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，我想知道有關AttachmentTbl多個Attachment s的給出ReporterTbl.ID，多少Attachment小號我有嗎？

表結構：

ReporterTbl 

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

    AttachmentTbl: 

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

來源

2010-09-09 Nick Kahn

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

來源

2010-09-09 19:15:23 RedFilter

給出ReporterTbl.ID我多少附件有。

豈不只是：

select count(*) from AttachmentTbl where id = @ID;

來源

2010-09-09 19:18:01

當然，如果你想要一個記者。 – 2010-09-09 19:20:23

但這就是他要求的.... – 2010-09-09 19:21:18

如果你想獲得的所有字段報道（不僅ID），這會爲你節省JOIN：

SELECT r.*, 
     (
     SELECT COUNT(*) 
     FROM AttachmentTbl a 
     WHERE a.id = r.id 
     ) AS AttachmentCount 
FROM ReportedTbl r

來源

2010-09-09 19:26:50 Quassnoi

如何計算一對多的關係

回答

相關問題