alter table mieter
    add column iban varchar(34);

delimiter //

create or replace function format_iban(p_iban varchar(34)) returns varchar(34)
begin
    declare v_country varchar(2);
    declare v_part1 varchar(4);
    declare v_part2 varchar(4);
    declare v_part3 varchar(4);
    declare v_part4 varchar(4);
    declare v_part5 varchar(4);
    declare v_part6 varchar(2);
    declare v_result varchar(34);

    set v_country = substring(p_iban from 1 for 2);

    if (v_country = 'DE') then
        set v_part1 = substring(p_iban from 3 for 2);
        set v_part2 = substring(p_iban from 5 for 4);
        set v_part3 = substring(p_iban from 9 for 4);
        set v_part4 = substring(p_iban from 13 for 4);
        set v_part5 = substring(p_iban from 17 for 4);
        set v_part6 = substring(p_iban from 21 for 2);
        set v_result = concat(v_country, ' ', v_part1, ' ', v_part2, ' ', v_part3, ' ',
                              v_part4, ' ', v_part5, ' ', v_part6);
    else
        set v_result = p_iban;
    end if;

    return v_result;
end;
//

create or replace function check_iban(p_iban varchar(34)) returns boolean
begin
    declare v_country varchar(2);
    declare v_result boolean;
    declare v_rearranged_iban varchar(36);
    declare v_numeric_iban decimal(36, 0);
    declare v_numeric_result decimal(36, 0);

    set v_country = substring(p_iban from 1 for 2);

    if (v_country = 'DE') then
        set v_rearranged_iban = concat(substring(p_iban from 5), '1314', substring(p_iban from 3 for 2));
        set v_numeric_iban = cast(v_rearranged_iban as decimal(36, 0));
        set v_numeric_result = v_numeric_iban % 97;
        if (v_numeric_result = 1) then
            set v_result = TRUE;
        else
            set v_result = FALSE;
        end if;
    else
        set v_result = TRUE;
    end if;

    return v_result;
end;
//


delimiter ;