Поиск дубликатов в MySQL

case-insensitive collation (_ci):
select distinct
    md5(column) as hash, column, count(*) as c
from
    table
group by
    hash
having
    c > 1
binary collation (_bin):
select
    column, count(*) as c
from
    table
group by
    column
having
    c > 1
How to find duplicates in MySQL