Sql Update on Row_Number

Question

I have a table with few columns say,

FirstName, Lastname, Phonenumber, Accesslevel
AA ,          BB  ,    +447000000000,  AL1
CC ,          DD ,     +447800000000 , AL2
AA  ,         BB  ,    +447000000000 , AL3

If the phoneNumbers and Lastname are same, I want the below results (I mean I need to Update the table instead of just select)

FirstName, Lastname, Phonenumber, Accesslevel
AA ,          BB  ,    +447000000000,  AL1, AL3
CC ,          DD ,     +447800000000 , AL2
AA  ,         BB  ,    +447000000000 , AL3

The script I have doesn't do what i Want,

UPDATE [dbo].[Table]
SET [AccessLevel] = stuff ( ( SELECT
                          ', ' + [ExtAccessLevelIDList]
                  FROM
                          [Table] t1
                  where t1.PhoneNumber = t2.PhoneNumber
        FOR XML PATH ( '' ) ) , 1 , 1, '' )
from [Table] t2```

Answer 1

Well, if you care about both the telephone number and name, you need equality on both those columns:

UPDATE t2
    SET [AccessLevel] = STUFF( (SELECT ', ' + [ExtAccessLevelIDList]
                                FROM [Table] t1
                                WHERE t1.PhoneNumber = t2.PhoneNumber AND
                                      t1.LastName = t2.LastName
                                FOR XML PATH ( '' )
                               ), 1, 2, ''
                             )
    FROM (SELECT t2.*,
                 ROW_NUMBER() OVER (PARTITION BY LastName, PhoneNumber ORDER BY (SELECT NULL)) as seqnum
          FROM [Table] t2
         ) t2
    WHERE seqnum = 1;

Note:

More recent versions of SQL Server support string_agg() which makes this much simpler:

update [table]
    set AccessLevel = tt.accesslevel
    from (select phonenumber, lastname,
                 string_agg(ExtAccessLevelIDList, ', ') as accesslevel
          from [table]
          group by phonenumber, lastname
         ) tt
    where tt.phonenumber = [table].phonenumber and
          tt.lsatname = [table].lastname;