Question

Using SQL Server 2005 / 2008 I have a table BB_MEDIAOBJECT (Id, ...), which includes several other data-fields for mediaobjects, a table BB_COLLECTION (Id, Name, Description) in which approx 30 collections are defined, and a table BB_MEDIAOBJECT_COLLECTION (MediaObjectId, CollectionId), Which lists all items in each collection.

Please help me with defining a SQL query that gives me the first 10 mediaobjects for each collection.

Based upon the answer supplied by Marc, I’ve ended up with the following end result, in which the query now correctly displays the 10 most recently modified items:

;WITH PartitionedComponents AS  
(  
    SELECT  
        CollectionID = c.ID,  
        c.Name,  
        c.Description, 
        MediaObjectId = m.ID, 
        ROW_NUMBER() OVER(PARTITION BY c.ID ORDER BY m.modifiedby DESC) AS 'RowNum' 
    FROM  
        dbo.BEELDBANK_COLLECTION c 
    INNER JOIN 
        dbo.BEELDBANK_MEDIAOBJECT_COLLECTION mc ON mc.CollectionId = c.ID 
    INNER JOIN 
        dbo.BEELDBANK_MEDIAOBJECT m ON mc.MediaObjectId = m.Id 
) 
SELECT  
    CollectionID,  
    Name,  
    Description, 
    MediaObjectId 
FROM  
    PartitionedComponents 
WHERE 
    RowNum <= 10

Answer 1

One approach would be to use a CTE (Common Table Expression). You can partition your data by some criteria – i.e. your Id for the collection – and have SQL Server number all your rows starting at 1 for each of those partitions, ordered by some other criteria – i.e. probably Id for your media object (you didn’t specify exactly – you want the 10 first objects – but you didn’t say what these would be ordered by; first ten always implies there must be some order – change my CTE query as needed for your case!)

So try something like this:

;WITH PartitionedComponents AS
(
   SELECT 
       CollectionID = c.ID, 
       c.Name, 
       c.Description,
       MediaObjectId = m.ID,
       ROW_NUMBER() OVER(PARTITION BY c.ID ORDER BY m.ID DESC) AS 'RowNum'
   FROM 
       dbo.BB_Collection c
   INNER JOIN
       dbo.BB_MEDIAOBJECT_COLLECTION mc ON mc.CollectionId = c.ID
   INNER JOIN
       dbo.BB_MEDIAOBJECT m ON mc.MediaObjectId = m.Id
   WHERE
       ......
)
SELECT 
   CollectionID, 
   Name, 
   Description,
   MediaObjectId
FROM 
   PartitionedComponents
WHERE
   RowNum <= 10

Here, I am selecting the first ten entries for each “partition” (i.e. for each Id) – ordered in a descending fashion by the Id (of MediaObjects).

Does that approach what you’re looking for??