Question

Is it possible to perform a JOIN sub query against a Common Table Expression? If not, then can someone let me know how to perform what I am trying to do below? Examples would be excellent.

For example:

LEFT JOIN (

            ;WITH [UserDefined]
                AS (SELECT *, -- Make sure we get only the latest revision.
                        ROW_NUMBER() OVER (PARTITION BY [ID]
                                                ORDER BY [RevisionNumber] DESC) AS RN
                    FROM [syn_Change])

            SELECT [UserDefined].[ID]
                ,[UserDefined].[ChangeNumber]
                ,[UserDefined].[Usr_CoResponsibility]
                ,[UserDefined].[Usr_StarFlowStatus]

            FROM [UserDefined]
            WHERE (RN = 1) 

            ) [UserColumns]
ON [UserColumns].[ChangeNumber] = [CTE].[ChangeNumber]

Here is my full query:

;WITH CTE
    AS (SELECT *, -- Make sure we get only the latest revision.
            ROW_NUMBER() OVER (PARTITION BY [ItemID]
                                    ORDER BY [RevisionNumber] DESC) AS RN
        FROM [dw_Change])

SELECT [CTE].[ItemID]
        ,[CTE].[ViewID]
        ,[CTE].[FolderItemID]
        ,[CTE].[RevisionNumber]
        ,[CTE].[ChangeNumber]
        ,[CTE].[Synopsis]
        ,[CTE].[Description]
        ,[CTE].[EnteredOn]
        ,[CTE].[Responsibility]
        --,[UserColumns].[Usr_CoResponsibility]
        --,[UserColumns].[Usr_StarFlowStatus]
        ,[CTE].[Status] -- This will display the human name on the front-end with code.
        ,[Users].[F7] AS [ResponsibilityName]
        ,[GroupName].[Name] AS [AppGroupName]
        ,[AppName].[Name] AS [AppName]
FROM CTE
LEFT JOIN [S3] [Users] ON [Users].[F0] = [CTE].[Responsibility]
LEFT JOIN (SELECT [Name], [ViewID]
            FROM [dw_Folder]
            WHERE ([FolderItemID] = -1)) [GroupName]
ON [GroupName].[ViewID] = [CTE].[ViewID]

LEFT JOIN (SELECT [Name], [ItemID]
            FROM [dw_Folder]
            WHERE ([FolderItemID] <> -1)) [AppName]
ON [AppName].[ItemID] = [CTE].[FolderItemID]

LEFT JOIN (

            ;WITH [UserDefined]
                AS (SELECT *, -- Make sure we get only the latest revision.
                        ROW_NUMBER() OVER (PARTITION BY [ID]
                                                ORDER BY [RevisionNumber] DESC) AS RN
                    FROM [syn_Change])

            SELECT [UserDefined].[ID]
                ,[UserDefined].[ChangeNumber]
                ,[UserDefined].[Usr_CoResponsibility]
                ,[UserDefined].[Usr_StarFlowStatus]

            FROM [UserDefined]
            WHERE (RN = 1) 

            ) [UserColumns]
ON [UserColumns].[ChangeNumber] = [CTE].[ChangeNumber]

WHERE (RN = 1)

Thanks so much!

Answer 1

When you define a CTE you’re doing so before any of the rest of the query. So you can’t write:

LEFT JOIN (
  ;WITH CTE
  ...
)

As a quick aside, the reason people put ; in front of WITH is because all previous statements need to be terminated. If developers could get in the habit of terminating all SQL statements with ; then it wouldn’t be necessary, but I digress…

You can write multiple CTEs like so:

WITH SomeCTE AS (
  SELECT ...
  FROM ...
), AnotherCTE AS (
  SELECT ...
  FROM ...
)
SELECT *
FROM SomeCTE LEFT JOIN
     AnotherCTE ON ...
;