create or replace function ibge_dv(codigo char(6))
returns char(1) as $$

    select ((10 - resto) * (resto != 0)::int)::char(1)
    from (
        select
            (
                a135 +
                left(a2, 1)::int + right(a2, 1)::int +
                left(a4, 1)::int + right(a4, 1)::int +
                left(a6, 1)::int + right(a6, 1)::int
            ) % 10 as resto
        from (
            select
                a[1] + a[3] + a[5] as a135,
                to_char(a[2] * 2, 'FM09') as a2,
                to_char(a[4] * 2, 'FM09') as a4,
                to_char(a[6] * 2, 'FM09') as a6
            from (
                select string_to_array(codigo, null)::integer[] as a
            ) s
        ) s
    ) s
    ;

$$ language sql;