Max date in view on left outer join

Question

Thanks to a previous question, I found out how to pull the most recent data based on a linked table. BUT, now I have a related question.

The solution that I found used row_number() and PARTITION to pull the most recent set of data. But what if there's a possibility for zero or more rows in a linked table in the view? For example, the table FollowUpDate might have 0 rows, or 1, or more. I just want the most recent FollowUpDate:

SELECT 
    EFD.FormId
    ,EFD.StatusName
    ,MAX(EFD.ActionDate)
    ,EFT.Name AS FormType
    ,ECOA.Account AS ChargeOffAccount
    ,ERC.Name AS ReasonCode
    ,EAC.Description AS ApprovalCode
    ,MAX(EFU.FollowUpDate) AS FollowUpDate
FROM (
  SELECT EF.FormId, EFD.ActionDate, EFS.Name AS StatusName, EF.FormTypeId, EF.ChargeOffId, EF.ReasonCodeId, EF.ApprovalCodeId, 
         row_number() OVER ( PARTITION BY EF.FormId ORDER BY EFD.ActionDate DESC ) DateSortKey
    FROM Extension.FormDate EFD INNER JOIN Extension.Form EF ON EFD.FormId = EF.FormId INNER JOIN Extension.FormStatus EFS ON EFD.StatusId = EFS.StatusId
  ) EFD
    INNER JOIN Extension.FormType EFT ON EFD.FormTypeId = EFT.FormTypeId
    LEFT OUTER JOIN Extension.ChargeOffAccount ECOA ON EFD.ChargeOffId = ECOA.ChargeOffId
    LEFT OUTER JOIN Extension.ReasonCode ERC ON EFD.ReasonCodeId = ERC.ReasonCodeId
    LEFT OUTER JOIN Extension.ApprovalCode EAC ON EFD.ApprovalCodeId = EAC.ApprovalCodeId
    LEFT OUTER JOIN (Select EFU.FormId, EFU.FollowUpDate, row_number() OVER (PARTITION BY EFU.FormId ORDER BY EFU.FollowUpDate DESC) FUDateSortKey FROM Extension.FormFollowUp EFU INNER JOIN Extension.Form EF ON EFU.FormId = EF.FormId) EFU ON EFD.FormId = EFU.FormId
WHERE EFD.DateSortKey = 1
GROUP BY
    EFD.FormId, EFD.ActionDate, EFD.StatusName, EFT.Name, ECOA.Account, ERC.Name, EAC.Description, EFU.FollowUpDate
ORDER BY 
    EFD.FormId

If I do a similar pull using row_number() and PARTITION, I get the data only if there is at least one row in FollowUpDate. Kinda defeats the purpose of a LEFT OUTER JOIN. Can anyone help me get this working?

Answer 1

It's pretty hard to guess what's going on without table definitions and sample data.

Also, this is confusing: "the table FollowUpDate might have 0 rows" and you "want the most recent FollowUpDate." (especially when there is no table named FollowUpDate) There is no "most recent FollowUpDate" if there are zero FollowUpDates.

Maybe you want

WHERE <follow up date row number> in (1,NULL)

Answer 2

I rewrote your query - you had unnecessary subselects, and used row_number() for the FUDateSortKey but didn't use the column:

SELECT t.formid,
   t.statusname,
   MAX(t.actiondate) 'actiondate',
   t.formtype,
   t.chargeoffaccount,
   t.reasoncode,
   t.approvalcode,
   MAX(t.followupdate) 'followupdate'
FROM (
   SELECT t.formid, 
          fs.name 'StatusName',
          t.actiondate,
          ft.name 'formtype',
          coa.account 'ChargeOffAccount',
          rc.name 'ReasonCode',
          ac.description 'ApprovalCode',
          ffu.followupdate,
          row_number() OVER (PARTITION BY ef.formid ORDER BY t.actiondate DESC) 'DateSortKey'
     FROM EXTENSION.FORMDATE t 
     JOIN EXTENSION.FORM ef ON ef.formid = t.formid
     JOIN EXTENSION.FORMSTATUS fs ON fs.statusid = t.statusid
     JOIN EXTENSION.FORMTYPE ft ON ft.formtypeid = ef.formtypeid
LEFT JOIN EXTENSION.CHARGEOFFACCOUNT coa ON coa.chargeoffid = ef.chargeoffid
LEFT JOIN EXTENSION.REASONCODE rc ON rc.reasoncodeid = ef.reasoncodeid
LEFT JOIN EXTENSION.APPROVALCODE ac ON ac.approvalcodeid = ef.approvalcodeid
LEFT JOIN EXTENSION.FORMFOLLOWUP ffu ON ffu.formid = t.formid) t
    WHERE t.datesortkey = 1
 GROUP BY t.formid, t.statusname, t.formtype, t.chargeoffaccount, t.reasoncode, t.approvalcode
 ORDER BY t.formid

The change I made to allow for FollowUpDate was to use a LEFT JOIN onto the FORMFOLLOWUP table - you were doing an INNER JOIN, so you'd only get rows with FORMFOLLOWUP records associated.

Answer 3

I figured it out. And as usual, I need a nap. I just needed to change my subselect to something I would swear I'd tried with no success:

SELECT field1, field2     
FROM Table1 t1    
LEFT JOIN (    
      SELECT field3, max(dateColumn)    
      FROM Table2    
      GROUP BY    
            field3    
) t2    
ON (t1.field1 = t2.field3)