SQL Server conditional query for a master detail query result - sql

Question

I have this question. Let's see the query:
SELECT
D.DocumentName,
D.Title,
D.Description,
V.Version,
CASE
WHEN V.State = 'PUB' THEN 'PUBLISHED'
WHEN V.State = 'UNP' THEN 'UNPUBLISHED'
WHEN V.State IS NULL THEN 'NOT PUBLISHED'
ELSE ''
END AS State
FROM
Document D
LEFT JOIN
DocumentVersion V ON D.IdDocument = V.IdDocumentVersion
This is a typical master-detail table (Document-DocumentVersion). A Document can have one or more DocumentVersions or none. A DocumentVersion state can be PUBLISHED or UNPUBLISHED. The PUBLISHED one DocumentVersion can exist just once for a Document (this is controlled by application), but there can exist many UNPUBLISHED, or all DocumentVersions are UNPUBLISHED. NOT PUBLISHED doesn't exist, it's just a word in the query result when there's no DocumentVersion record for a Document, that's the reason for the LEFT JOIN.
So my question is: how can I make the query accomplish the next rules?
If a DocumentVersion state is PUB, ignore the others, I mean don't show the UNP ones in the query result for this Document
If a DocumentVersion state is UNP (and here can be many UNP), then show only the one with the highest date of Unpublish (DocumentVersion table has a UnPublishDate column), this rule applies just when there's no PUB DocumentVersion for the document
I would appreciate any help you can give me, thanks guys.

Answer 1

select *
from Document D
left outer join
(select *,
row_number()over(partition by IdDocumentVersion order by state asc, UnPublishDate desc) as row
from DocumentVersion) V
on D.IdDocument = V.IdDocumentVersion
and V.row = 1
State asc is a bit of a hack by the way that just happens to work in this case. You might want to be more explicit with a 'case when' (see Gordon's answer).

Answer 2

This is a prioritization query. You can do it using row_number() or rank():
select d.*, dv.*
from d left join
(select dv.*,
row_number() over (partition by dv.IdDocument
order by (case when dv.state = 'PUB' then 1
when dv.state = 'UNP' then 2
else 3
end)
) as seqnum
from documentversion dv
) dv
on dv.IdDocument = d.IdDocument and
seqnum = 1;
Note: I don't think the join condition is correct in your question.