CREATE FUNCTION comprovar_fechas_salarios (from_date DATE, to_date DATE, empleado INT(11)) RETURNS TINYINT(1) DETERMINISTIC
  BEGIN
  DECLARE respuesta TINYINT(1) DEFAULT 1;
    DECLARE done INT(1) DEFAULT 0;
    DECLARE old_from_d DATE;
    DECLARE old_to_d DATE;
    DECLARE emp_n INT(11);
    DECLARE salary INT(11);
    DECLARE salarios_emp CURSOR FOR SELECT * from salaries where emp_no = empleado;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;


    OPEN salarios_emp;
    l1:LOOP
    FETCH salarios_emp INTO emp_n, salary, old_from_d, old_to_d;
    IF done = 1 OR respuesta = 0 THEN
        CLOSE salarios_emp;
      LEAVE l1;
    END IF;
        IF from_date BETWEEN old_from_d AND old_to_d THEN
                    SET respuesta = 0;
                END IF;

                IF to_date BETWEEN old_from_d AND old_to_d THEN
                    SET respuesta = 0;
                END IF;

                IF from_date < old_from_d AND to_date > old_to_d THEN
                    SET respuesta=0;
                END IF;
    END LOOP l1;

        RETURN respuesta;

  END;

CREATE TRIGGER salario_ins BEFORE INSERT ON salaries FOR EACH ROW
  BEGIN
        IF comprovar_fechas_salarios (new.from_date, new.to_date, new.emp_no) = 0 THEN
            SIGNAL SQLSTATE '45000' SET message_text = "FECHAS SOLAPADAS";
        END IF;
  END;


CREATE TRIGGER salario_upd BEFORE UPDATE ON salaries FOR EACH ROW
  BEGIN
        IF comprovar_fechas_salarios (new.from_date, new.to_date, new.emp_no) = 0 THEN
            SIGNAL SQLSTATE '45000' SET message_text = "FECHAS SOLAPADAS";
        END IF;
  END;