I have two tables @Cust and @Bh. I need to take the last records from the @Bh table by the "loaddate" field and if there are no matches then insert the records.
@Cust:
DECLARE @Cust TABLE(
    Custnumber INT,
    Flag NVARCHAR(10),
    data NVARCHAR(10),
    status NVARCHAR(10),
    loaddate DATETIME
)
INSERT @Cust (Custnumber
                ,Flag
                ,data
                ,status
                ,loaddate)
VALUES (123,N'Y',N'20170117',N'Test','2018-11-15 15:35:26.393')
@Bh:
DECLARE @Bh TABLE(
    Custnumber INT,
    Flag NVARCHAR(10),
    data NVARCHAR(10),
    status NVARCHAR(10),
    loaddate DATETIME
)
INSERT @Bh (Custnumber
                ,Flag
                ,data
                ,status
                ,loaddate)
VALUES (123,N'Y',N'20170117',N'','2018-11-09 15:35:26.393')
,(123,N'Y',N'20170117',N'Tests','2018-11-10 15:35:26.393')
,(123,N'Y',N'20170117',N'','2018-11-15 15:35:26.393')
,(123,N'Y',N'20170117',N'Test','2018-11-15 15:35:26.393')
Result:
INSERT INTO @Bh(Custnumber
                ,Flag
                ,data
                ,status
                ,loaddate) 
SELECT DISTINCT PC.Custnumber
                ,PC.Flag
                ,PC.data
                ,PC.status
                ,PC.loaddate
FROM @Bh  AS BH
    INNER JOIN @Cust AS PC ON PC.Custnumber = BH.Custnumber
                                        AND (ISNULL(PC.Flag, '''')  <> ISNULL(BH.Flag, '''')
                                        OR   ISNULL(PC.data, '''')  <> ISNULL(BH.data, '''')
                                        OR   ISNULL(PC.status, '''')  <> ISNULL(BH.status, '''')) 
WHERE BH.loaddate = (SELECT MAX(loaddate) FROM @Bh AS BH2 WHERE BH.[Custnumber] = BH2.[Custnumber])';
Because I have not quite the right condition, then insert the record due to the fact that row number 3 is different from the entry in the table @Cust and as a result is added to the table @Bh
Here is a solution that I came up with and it fits my cases, but maybe there is some simpler solution?
WHERE   NOT EXISTS(SELECT 1 FROM @Bh AS BH2 WHERE PC.Custnumber = BH2.Custnumber AND PC.Flag = bh2.Flag GROUP BY BH2.Custnumber HAVING CONVERT(varchar(10), max(bh2.[loaddate]), 101) = (SELECT CONVERT(varchar(10), max([loaddate]), 101) FROM @Bh AS BH3 WHERE BH3.Custnumber = BH2.Custnumber))
        OR NOT EXISTS(SELECT 1 FROM @Bh AS BH2 WHERE PC.Custnumber = BH2.Custnumber AND PC.data = bh2.data GROUP BY BH2.Custnumber HAVING CONVERT(varchar(10), max(bh2.[loaddate]), 101) = (SELECT CONVERT(varchar(10), max([loaddate]), 101) FROM @Bh AS BH3 WHERE BH3.Custnumber = BH2.Custnumber))
        OR NOT EXISTS(SELECT 1 FROM @Bh AS BH2 WHERE PC.Custnumber = BH2.Custnumber AND PC.status = bh2.status GROUP BY BH2.Custnumber HAVING CONVERT(varchar(10), max(bh2.[loaddate]), 101) = (SELECT CONVERT(varchar(10), max([loaddate]), 101) FROM @Bh AS BH3 WHERE BH3.Custnumber = BH2.Custnumber))
