query distinct mysql

I have two tables:

students (student_id, id_carrera, nro_doc ... rterc, eterc) PK (student_id, id_carrera).

debts (rterc, eterc, date_of_voice, number_of_voice, amount, expiration ...) The table does not have debts.

The field eterc is equal to the document number.

To get rid of the student's debts I use a sp like this:

CREATE DEFINER='root'@'localhost' PROCEDURE 'ALU_DEUDAS'(
    IN p_alumno varchar(50),
    IN p_rterc char(2),
    IN p_eterc char(15)
)
BEGIN
if p_rterc != '' and p_eterc != '' then
    SELECT d.* 
        FROM camp_deuda as d 
            INNER JOIN camp_alumnos as a 
                ON a.calu_rterc = d.rterc and a.calu_eterc = d.eterc
        WHERE a.calu_id_alumno = p_alumno AND d.rterc = p_rterc AND d.eterc = p_eterc;
end if;
END

It works perfectly, the problem is when the student is enrolled in several races. He repeats the invoices according to the careers that the student has.

How can I solve it? I thought about doing a select distinct nro_factura . I do not know what you think. Thank you very much