Because you don't want duplicate rows.
This works for me in Oracle. YMMV. Just change "table_name" to the table you wish to query.
Happy deduping!
select * from
table_name -- change table name
where id_number in (SELECT id_number
FROM (SELECT ROW_NUMBER()
OVER(PARTITION BY id_number ORDER BY id_number asc) AS r,
f.* FROM (select * from
table_name -- change table name
) f) x WHERE x.r = 2)
order by id_number
