How to find the difference between dates within the same column using Netezza

I am trying to solve the following challenge:
1) If a patient visits the ER within 48 hours, I want to flag that as 1.
2) If the same patient visits the ER again after 48 hours, I want to flag that as 2.
3) Each subsequent visit must be flagged as 3, 4, 5 etcetera after the first 48 hours.

the sql code below works fine but we are now using netezza database and the code below does not work in netezza so i would like to modify it so it can work in netezza.  I believe the main thing that does not work here is the datediff function here.  here is my sql code:

SET NOCOUNT ON
GO

    DECLARE @DataSource TABLE
    (
         [ATIENT_ID] TINYINT
        ,[ADMIT_DATE] DATE
        ,[LOCATION] VARCHAR(3)
    )

    INSERT INTO @DataSource ([ATIENT_ID], [ADMIT_DATE], [LOCATION])
    VALUES (33, '1-10-2014', 'ER')
          ,(33, '1-11-2014', 'ER')
          ,(33, '1-15-2014', 'ER')
          ,(33, '1-17-2014', 'ER')
          ,(45, '2-15-2014', 'OBS')
          ,(45, '2-16-2014', 'OBS')
          ,(45, '2-20-2014', 'OBS')
          ,(45, '2-25-2014', 'OBS')
          ,(45, '2-27-2014', 'OBS')

    ;WITH DataSource ([ATIENT_ID], [ADMIT_DATE], [LOCATION], [DIFF_IN_HOURS])  AS
    (
        SELECT [ATIENT_ID]
              ,[ADMIT_DATE]
              ,[LOCATION]
              ,DATEDIFF(
                            HOUR
                           ,LAG([ADMIT_DATE], 1, NULL) OVER (PARTITION BY [ATIENT_ID], [LOCATION] ORDER BY [ADMIT_DATE] ASC)
                           ,[ADMIT_DATE]
                        )
        FROM @DataSource
    )
    SELECT [ATIENT_ID]
          ,[ADMIT_DATE]
          ,[LOCATION]
          ,ROW_NUMBER() OVER (PARTITION BY [ATIENT_ID], [LOCATION] ORDER BY [ADMIT_DATE] ASC)
    FROM DataSource
    WHERE [DIFF_IN_HOURS] >= 48
        OR [DIFF_IN_HOURS] IS NULL -- these are first records

SET NOCOUNT OFF
GO

Select allOpen in new window