Problem counting records

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Sir Hystrix - 30 Nov 2007 10:18 GMT

Hi,

I am struggling with a simple query, but I just don't see it.
I have the following example table.

Table Messages
ID Subject Reply_to
1 A 0
2 Ax 1
3 A 1
4 B 0
5 By 4
6 C 0

The table holds new messages as well as replies to messages.
Messages with Reply_to = 0 are top messages, the other messages are
replies to a top message. The subject of a reply message does not
necessarily have to be the same as the subject of the top message.

What I would like to have returned is this: a list of messages where
Reply_to = 0 and the number of replies to this message.

ID Subject Num_replies_to
1 A 2
4 B 1
6 C 0

Any assistance would be greatly appreciated.

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Manfred Sorg - 30 Nov 2007 12:13 GMT

Did you think of this:

select t1.ID, t1.Subject, count(1) as Num_replies_to
from tbl t1
left join tbl t2
on t2.Reply_to=t1.ID
where t1.Reply_to=0
group by t1.ID, t1.Subject

Bye, Manfred

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Dan Guzman - 30 Nov 2007 12:16 GMT

> What I would like to have returned is this: a list of messages where
> Reply_to = 0 and the number of replies to this message.

A subquery like the example below is one method.

SELECT
m.ID,
m.Subject,
(SELECT COUNT(*)
FROM dbo.Messages
WHERE Reply_to = m.ID
) AS Num_replies_to
FROM dbo.Messages AS m
WHERE Reply_to = 0

Signature

Hope this helps.

Dan Guzman
SQL Server MVP

> Hi,
>
[quoted text clipped - 24 lines]
>
> Any assistance would be greatly appreciated.

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Sir Hystrix - 30 Nov 2007 13:30 GMT

>> What I would like to have returned is this: a list of messages where
>> Reply_to = 0 and the number of replies to this message.
[quoted text clipped - 10 lines]
> FROM dbo.Messages AS m
> WHERE Reply_to = 0

I knew it was simple. It had to be simple. I just didn't see it.
Many thanks to both Dan and Manfred.

Cheers.

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