'How to count one to many relationships

ReporterTbl has a one to many relationship with AttachmentTbl.

In ReporterTbl, I have an ID (101) and I can have AttachmentTbl more than one Attachments related with 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
)

Basically, what I am trying to know is given ReporterTbl.ID, how many Attachments do I have?

Table structure:

 ReporterTbl

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

    AttachmentTbl:

    AttachmentId indentity
    Id {**FK to ReproterTbl**}
    Filename
    Content
    ...
sqlsql-server-2008


Solution 1:[1]

If you want to get all fields from Reported (not only ID), this will save you a JOIN:

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

Solution 2:[2]

given ReporterTbl.ID how many attachments i have.

Wouldn't it just be:

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

Solution 3:[3]

I had to group by the first element in the SELECT clause as well as the item I am aggregating on:

SELECT p.Name, COUNT(c.PersonId) AS Count
FROM People AS p
LEFT JOIN Contacts AS c
    ON (p.Id = c.PersonId)
GROUP BY c.PersonId, p.Name;

I am not really sure why I had to do this, it isn't the case when using SQLite, which is what I am used to.

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1 Quassnoi
Solution 2 James Curran
Solution 3 Michael Murphy

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