Find equal twin record postgresql - postgresql

Question

I have a table company with 60 columns. The goal is to create a tool to find, compare and eliminate duplicates in this table.
Example: I have a record with id 22 and I know it has a twin because I run this (simplified code):
SELECT min(co_id),co_name,count(*) FROM co
GROUP BY co_name
HAVING count(*) > 1
The result shows there are one twin (count 2) and I get the oldest id by min(co_id)
My question is how I search for the twin co_id? Just passing the oldest id?
Something like:
SELECT co_id FROM co
WHERE co_name EQUAL TO co_id='22'
LIMIT 2
Sample data:
id co_name
22 Volvo
23 Volvo
24 Ford
25 Ford
I know id 22 and I want to search for the twin 23 based on the content of 22.
The closest I found is this. Which is far from generic. And a nightmare for comparing 60 field:
SELECT id,
(SELECT max(b.id) from co b
WHERE a.co_name = b.co_name
LIMIT 1) as twin
FROM co a
WHERE id='22'
How do I do this in a more simple and generic way? I just want the twin record co_id.
Thank you in advance!

Answer 1

select max_co,co_name from (
select max(co_id) max_co,min(co_id) min_co,co_name from co
group by co_name having count(*)>1) where min_co=(your old co id as input);

Answer 2

You can join your table with itself:
SELECT c1.*
FROM
co_name c1 INNER JOIN co_name c2
ON c1.co_name=c2.co_name
AND c1.id>c2.id
this will return all duplicated records (but not the original record with the lowest id). Or since you're using Postgresql you can use a window function:
SELECT *
FROM (
SELECT
id,
co_name,
row_number() OVER (PARTITION by co_name ORDER BY id) as row
FROM
co_name
) s
WHERE
row>1;
Please see an example here.
If you want to compare multiple columns, the JOIN solution would be more flexible. I don't know exactly how you want to compare your columns and how you exactly define "twin" rows, but you a query like this should help:
SELECT c1.*
FROM
co_name c1 INNER JOIN co_name c2
ON (
c1.co_name=c2.co_name
OR c1.co_city=c2.co_city
OR c1.co_owner=c2.co_owner
OR ...
) AND c1.id>c2.id
if you just want duplicated records of id=22 then you can try with this:
SELECT c1.*
FROM
co_name c1 INNER JOIN co_name c2
ON c1.co_name=c2.co_name
AND c1.id>c2.id
WHERE
c2.id=22
or if you just want a single twin, comparing 60 columns, you can try with this query:
SELECT MIN(ID) as Twin /* or MAX(ID), depending what you're after */
FROM
co_name c1 INNER JOIN co_name c2
ON (
c1.co_name=c2.co_name
OR c1.co_city=c2.co_city
OR c1.co_owner=c2.co_owner
OR ...
) AND c1.id>c2.id
WHERE
c2.id=22

Answer 3

I found one solution that is working on 60 columns if I use variables in stead of hardcode in the query. Thanks everybody for all input. Some of them were about the same track.
SELECT id,
(SELECT max(b.id) from co b
WHERE concat(a.co_name,etc) = concat(b.co_name,etc)
LIMIT 1) as twin
FROM co a
WHERE id='22'
Not the best one, but fetch one twin at a time. And it is far from generic. Thanks for pointing me in the right direction. A generic solution would be nicer.