SQL Server + Selecting records with sub tables items

Question

I have a post table which has a photo sub table, so one post can have many photos, one of the photo table column is [Priority].

I need to select records from the post table with only the photo that has a top priority in another table:

So the result should be like:

Photo  Post
pic1   Article1
picX   Article2

Currently my results shows as

Photo  Post
pic1   Article1
pic2   Article1
picX   Article2

with this query:

 SELECT  [Photo], 
         [PostTitle]
 FROM [Post] sp
 INNER JOIN [PostPhotos] spp
 ON (sp.AutoId = spp.PostId)
 WHERE sp.[AutoId] IN (SELECT [PostID] 
                       FROM [Favorites] 
                       WHERE [UserId] = 'UserXXX')

I tried a join query without success:

 SELECT photo, 
        [PostTitle],
        [AskingPrice]
 FROM (SELECT sp.[AutoId], 
              [PostTitle] 
       FROM [SellPost] sp
       WHERE sp.[AutoId] IN (SELECT [PostID] 
                             FROM [Favorites] 
                             WHERE [UserId] = 'UserId') )a
 full OUTER JOIN(SELECT TOP 1 [PostId], 
                        [photo] 
                 FROM [PostPhotos] spp 
                 WHERE PostId IN (SELECT [PostID] 
                                  FROM [Favorites] 
                                  WHERE [UserId] = 'UserXXX') 
                 ORDER BY [Priority] ASC )b
  on (a.AutoId = b.PostId)
  order by a.AutoId; 

My Tables:

Table Post
PostId, PostTitle

Table PostPhotos
AutoId, PostId, Photo, Priority --> 1 post can have many photos

Can someone please kindly assist. Thanks.

Answer 1

Try with this hint:

SELECT [p].[PostId],[PostTitle],[Photo] FROM [Post] p
INNER JOIN [PostPhots] pp
ON [p].[PostId] = [pp].[PostId] 
WHERE [p].[PostId] 
IN (SELECT TOP 1 [PostId] FROM [PostPhotos] ORDER BY [Priority] DESC)

Answer 2

A few things are unclear from your description (like what is AutoId , what is the primary key of PostPhotos and what are you doing with Favorites /what does that table look like). But here is the general idea:

WITH RankedPhotos AS (
  SELECT
    PostId,
    AutoId, -- I'm assuming this is the primary key of PostPhotos?
    RANK() OVER (PARTITION BY AutoId, PostId ORDER BY Priority ASC) AS PhotoRank
  FROM
    Post p JOIN
    PostPhotos pp ON
      p.PostId = pp.PostId
), TopPhotos AS (
  SELECT
    PostId,
    AutoId
  FROM
    RankedPhotos
  WHERE
    PhotoRank = 1
)
SELECT
  PostTitle,
  Photo
FROM
  RankedPhotos r JOIN
  Post p ON
    r.PostId = p.PostId JOIN
  PostPhotos pp ON
    r.AutoId = p.AutoId

Of course you could unwrap the CTE and use nested subqueries (you could also probably get rid of TopPhotos completely), but this is probably easier to see/understand.

The basic idea is:

• In RankedPhotos , "rank" all of the Post / PostPhoto pairs
• In TopPhotos filter the IDs down to the ones with the highest ranks
• Join back to the original tables to get the records you actually want

Obviously if you need to filter by some other criteria (like a user) that will need to be added. It's best to add that as early in the process as possible (ie in RankedPhotos ) since otherwise the database may end up doing more work than it needs.

Answer 3

Sub queries not my strongest point but I think the below may work:

SELECT t1.Photo, t2.PostTitle
FROM Post t2
   INNER JOIN PostPhotos t1 ON (t2.PostID = t1.PostID)
WHERE t1.AutoID IN (SELECT TOP 1 d.AutoID, d.PostID
                        FROM PostPhotos As d
                        WHERE d.PostID = t1.PostID 
                        ORDER BY d.Priority, d.AutoID)

Note the addition of d.AutoID in the ordering of the subquery, this is in case two photos have the same priority.

EDIT I learnt a lot of what I know about subqueries here

Answer 4

Sorry for the mistakes in my post, I think I have been thinking too deep, all I need was:

   SELECT [p].[AutoId], [PostTitle], [Photo] FROM [Post] p
      INNER JOIN [PostPhotos] pp
      ON [p].[AutoId] = [pp].[PostId] 
      WHERE p.[AutoId] IN (SELECT [PostID] FROM [Favorites] WHERE [UserId] = @UserId)
      AND [Priority] = 1

Answer 5

SELECT  B.Photo,A.[PostTitle]
FROM    [Post]  A   INNER JOIN
        (SELECT AutoId,PostId,Photo,Priority
        FROM    PostPhotos
        WHERE   Priority =1) B ON A.[PostId] = B.[PostId]

I would do it in this way, and both of inner join and left join can get the result you want.