SQL Query return latest date with additional information from tables

Question

I have 5 tables and columns pertinent to this query:

• Dogs (ID, CallName, Color, Sex, Chipnumber, BreedID)
• Breed (ID, Name)
• Status (ID, Status, OwnedOnPremises)
• DogsStatus (ID, DogsID, StatusID, StatusDate, Note, ContactsID)
• Contacts (ID, Name)

I am wanting a result of all dogs and their LATEST status. For a test I am using the following records:

• Dogs (251, Tank, Fawn, M, 14410784, 23) (266, Bonnie, Brindle, 14964070, 23)
• Breed (23, Mastiff)
• Status (3, Sold) (4, Given Away) (7, Purchased) (9, Returned)
• DogsStatus (29, 251, 3, 2013-10-12, 5) (39, 251, 9, 2013-11-10, 17) (146, 251, 4, 2014-01-10, 7) (40, 266, 7, 2013-10-30, 1)
• Contacts (1, Person1) (5, Person5) (7, Person7) (17, Person17)

So far I have:

SELECT 
    d.CallName, b.Name AS 'Breed', d.Color, d.Sex, d.ChipNumber
FROM 
    Dogs d
JOIN 
   (SELECT 
        DogsID, MAX(StatusDate) as MaxStatusDate 
    FROM DogsStatus 
    GROUP BY DogsID) mds ON mds.DogsID = d.ID
JOIN 
   Breeds b ON b.ID = d.BreedID

This will return 2 unique records (1 for Tank and 1 for Bonnie), but whenever I try to get any other of the DogsStatus and/or Status info, I either return only one dog record, or all 3 of Tanks DogsStatus records.

Thanks in advance.

Answer 1

You'll need to join your MaxStatusDate to the DogsStatus table. That way you will only get the most recent status, in the case where you have multiple statuses. Something like

SELECT 
    d.CallName, b.Name AS 'Breed', d.Color, d.Sex, d.ChipNumber
FROM 
    Dogs d
innner join DogsStatus ds
  ON d.dogsid = ds.dogs_id
JOIN 
   (SELECT 
        DogsID, MAX(StatusDate) as MaxStatusDate 
    FROM DogsStatus 
    GROUP BY DogsID) mds ON mds.DogsID = d.ID
JOIN 
   Breeds b ON b.ID = d.BreedID
   AND mds.maxstatusdate = ds.statusdate

Something along those lines.

Answer 2

You're close. You just need to go back to the DogStatus table to get that full record. Note that I prefer CTEs for this, but your existing derived table (subquery) approach works just fine, too:

With StatusDates As
(

    SELECT 
        DogsID, MAX(StatusDate) as StatusDate 
    FROM DogsStatus 
    GROUP BY DogsID
), CurrentStatus As 
(
    SELECT ds.*
    FROM DogStatus ds
    INNER JOIN StatusDates sd ON sd.DogsID = ds.DogsID AND ds.StatusDate = sd.StatusDate
)
SELECT d.Name, b.Name As Breed, d.Color, d.Sex, d.ChipNumber
    , s.Status, cs.StatusDate, c.Name As ContactName
FROM Dogs d
INNER JOIN CurrentStatus cs ON cs.DogsID = d.ID
INNER JOIN Breed b on b.ID = d.BreedID
INNER JOIN Status s on s.ID = cs.StatusID
INNER JOIN Contact c on c.ID = cs.ContactID

You may want to use a LEFT join for some of those, and then change the select list to use coalesce() expressions to clean up the NULLs.

Answer 3

It would be something like this, I'm certain you'll be able to adapt it to your needs:

;with x as (
  select *, row_number() over(partition by d.DogsId order by StatusDate desc) as rn
  from Dogs d
  inner join DogsStatus on d.DogsId = ds.DogsId
)
select *
from x
where rn = 1