Update duplicate varchars to be unique in SQL database - sql

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

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.

Answer 2

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 3

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 4

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.