Finding Duplicate record

[sfast]

I have 7000 records in a table. There is a id_number field which is of type int. I want it to be primary key. But out of 7000 records there is one duplicate record.

When I do distinct id_number from table

it gives me total of 6999 records.

Can somebody guide me how to write the query to find out that one duplicate record.

[mark_roach]

select id_number, count(*) from table
group by id_number
having count(*) > 1

[sfast]

Thanks. The query worked.