使用DISTINCT和INNER JOIN的SQL

Question

I currently have 9 columns joined using INNER JOIN but i now want to remove the duplicates from column 1 which is CIFnumber .

If i use DISTINCT at the top of the query it does not function.

What could I do?

select distinct
    c.CIFNumber,c.FirstName,c.Surname,c.FamilyID,a.AccountID,
    b.V‌​aluationAmount,d.NAM‌​E,ad.ID_Number,f.PrP‌​lanner 
from
    CUSTOMERINFORMATIONFILETBL c
inner join ACCOUNTTBL a on c.CIFNumber=a.CIFNumber
inner join BALANCETBL b on a.AccountID=b.AccountID
inner join FAMILYTBL f on c.FamilyID= f.FamilyID
inner join DIVISION d on f.DIVISION=d.ID
inner join ADDRESSTBL ad on c.CIFNumber=ad.CIF 
where
    b.ValuationDate = '2017-09-30' and
    d.name = 'Wealth Management' and
    (
        ad.ID_Number= '' or
        ad.ID_Number is null or
        LEN(ad.ID_Number) < 13
    )

Answer 1

DISTINCT does function - it remove duplicates of the column set in specific SELECT statement. If DISTINCT did't remove duplicates for specific column in your column set it means that you have unique values in other columns.

If you need only one unique value from specific column and don't care about other column values, you can use window function.

   select *
   from (
    select c.CIFNumber,c.FirstName,..., 
    row_number() over (partition by c.CIFNumber order by [some logic]) as rn
    from...) as a 
    where rn = 1

Answer 2

You have two or more different values in at least one of your columns. If you dont care about some data you can use TOP 1 WITH TIES + ROW_NUMBER :

select top 1 with ties
            c.CIFNumber,
            c.FirstName,
            c.Surname,
            c.FamilyID,
            a.AccountID,
            b.V‌​aluationAmount,
            d.NAM‌​E,
            ad.ID_Number,
            f.PrP‌​lanner 
from
    CUSTOMERINFORMATIONFILETBL c
inner join ACCOUNTTBL a on c.CIFNumber=a.CIFNumber
inner join BALANCETBL b on a.AccountID=b.AccountID
inner join FAMILYTBL f on c.FamilyID= f.FamilyID
inner join DIVISION d on f.DIVISION=d.ID
inner join ADDRESSTBL ad on c.CIFNumber=ad.CIF 
where
    b.ValuationDate = '2017-09-30' and
    d.name = 'Wealth Management' and
    (
        ad.ID_Number= '' or
        ad.ID_Number is null or
        LEN(ad.ID_Number) < 13
    )
ORDER BY ROW_NUMBER() OVER (PARTITION BY c.CIFNumber, c.FirstName, c.Surname, c.FamilyID ORDER BY (SELECT NULL))

In my example I expect that c.CIFNumber, c.FirstName, c.Surname, c.FamilyID are unique.