thegunner thegunner - 3 months ago 12
SQL Question

SQL COUNT() / LEFT JOIN?

I have three tables: calls, attachments and notes and I want to display everything that's in the calls table, but also display whether a call has attachments and whether the call has notes. - by determining if there is an attachment or note record with a call_id in it. There could be notes and attachments, or there may not be but I would need to know.

Tables structure:

calls:

call_id | title | description


attachments:

attach_id | attach_name | call_id


notes:

note_id | note_text | call_id


If I write:

SELECT c.call_id
, title
, description
, count(attach_id)
FROM calls c
LEFT JOIN attachments a ON c.call_id = a.call_id
GROUP BY c.call_id
, title
, description


to give me a list of all calls and the number of attachments.

How can I also add in a column with the number of notes or a column which indicates that there is notes?

Any ideas?

Thanks.

Answer

For the count

SELECT 
     c.call_id, 
     title, 
     description, 
     count(DISTINCT attach_id) AS attachment_count , 
     count(DISTINCT note_id)  AS notes_count 
FROM calls c 
LEFT JOIN attachments a ON c.call_id = a.call_id 
LEFT JOIN notes n ON n.call_id = c.call_id 
GROUP BY c.call_id,title,description

Or for existence (will be more efficient if this is all you need)

SELECT 
     c.call_id, 
     title, 
     description, 
     count(attach_id) AS attachment_count , 
     case
        when exists (select * from notes n WHERE n.call_id = c.call_id) then
            cast(1 as bit)
        else
            cast(0 as bit)
    end as notes_exist
FROM calls c 
LEFT JOIN attachments a ON c.call_id = a.call_id 
GROUP BY c.call_id,title,description
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