Question

Yes, another SQL duplicates question 🙂

I have a SQL Server 2008 R2 table with multiple phone number columns, looking something like:

ID   Tel1   Tel2   Tel3   Tel4   Tel5   Tel6
 1    123    456    789   NULL   NULL   NULL
 2    123    456    123    123   NULL   NULL
 3    456    789    123    456   NULL   NULL

I’d like to remove the duplicate phone numbers from each row – for example, in row ID 2, I need to NULL Tel3 and Tel4, and in row 3 I need to NULL Tel4. I don’t need to check for duplicates between rows – the same phone number can exist between in multiple rows, just not in different columns in the same row.

Can anyone suggest the best way to get rid of these duplicates?

Answer 1

Sql Fiddle here.

update PhoneNumbers
   set Tel2 = case when Tel1 = Tel2 
                   then null 
                   else Tel2 end,
       Tel3 = case when Tel3 in (Tel1, Tel2) 
                   then null 
                   else Tel3 end,
       Tel4 = case when Tel4 in (Tel1, Tel2, Tel3) 
                   then null 
                   else Tel4 end,
       Tel5 = case when Tel5 in (Tel1, Tel2, Tel3, Tel4) 
                   then null 
                   else Tel5 end,
       Tel6 = case when Tel6 in (Tel1, Tel2, Tel3, Tel4, Tel5) 
                   then null 
                   else Tel6 end