Update duplicate varchars to be unique in SQL database

Question

I need to change a database to add a unique constraint on a table column, but the VARCHAR data in it is not unique.

How can I update those duplicate records so that each value is unique by adding a sequential number at the end of the existing data?

e.g. I would like to change 'name' to 'name1', 'name2', 'name3'

Answer 1

What database are you using?

In Oracle there is a:

NOVALIDATE Validates changes but does not validate data previously existing in the table

Example:

ALTER TABLE <table_name> ENABLE NOVALIDATE UNIQUE;

If you are not using Oracle then check the SQL reference for your respective database.

Answer 2

You could add another column to it... like

update mytable set mycolumn = concat(mycolumn, id) 
            where id in (<select duplicate records>);

replace id with whatever column makes mycolumn unique

Answer 3

Open a cursor on the table, ordered by that column. Keep a previous value variable, initialized to null, and an index variable initialized to 0. If the current value = the previous value, increment the index and append the index to the field value. if the current value <> the previous value, reset the index to 0 and keep the field value as is. Set the previous value variable = the current value. Move on to the next row and repeat.

Answer 4

Here are 2 examples with using the MS SQL SERVER flavor of sql.

Setup Example:

create table test (id int identity primary key, val varchar(20) )
 --id is a pk for the cursor so it can update using "where current of"

-- name a is not duplicated
-- name b is duplicated 3 times
-- name c is duplicated 2 times

insert test values('name a')
insert test values('name b')
insert test values('name c')
insert test values('name b')
insert test values('name b')
insert test values('name c')

Sql 2005\2008: ( Computed Table Expression )

begin tran; -- Computed table expressions require the statement prior to end with ;

with cte(val,row) as (

 select val, row_number() over (partition by val order by val) row
 --partiton is important. it resets the row_number on a new val
 from test 
 where val in ( -- only return values that are duplicated
  select val
  from test
  group by val
  having count(val)>1
 )
)
update cte set val = val + ltrim(str(row))
--ltrim(str(row)) = converting the int to a string and removing the padding from the str command.

select * from test

rollback

Sql 2000: (Cursor example)

begin tran

declare @row int, @last varchar(20), @current varchar(20)
set @last = ''
declare dupes cursor
 for
 select val 
 from test 
 where val in ( -- only return values that are duplicated
  select val
  from test
  group by val
  having count(val)>1
 )
 order by val

 for update of val

open dupes
fetch next from dupes into @current
while @@fetch_status = 0
begin
 --new set of dupes, like the partition by in the 2005 example
 if @last != @current
  set @row = 1

 update test
  --@last is being set during the update statement
  set val = val + ltrim(str(@row)), @last = val
  where current of dupes

 set @row = @row + 1

 fetch next from dupes into @current
end
close dupes
deallocate dupes

select * from test

rollback

I rolled back each of the updates because my script file contains both examples. This allowed me to test the functionality without resetting the rows on the table.