DELIMITER //

CREATE PROCEDURE udp_increase_salaries_by_country (country_name VARCHAR(40))
BEGIN
    DECLARE country_id INT;

    SELECT id INTO country_id
    FROM countries
    WHERE name = country_name;

    UPDATE workers w
    JOIN preserves p ON w.preserve_id = p.id
    JOIN countries_preserves cp ON p.id = cp.preserve_id
    SET w.salary = w.salary * 1.05
    WHERE cp.country_id = country_id;

    SELECT
        w.first_name,
        w.last_name,
        w.salary * 0.95 AS salary_before,
        w.salary AS salary_after
    FROM
        workers w
    JOIN
        preserves p ON w.preserve_id = p.id
    JOIN
        countries_preserves cp ON p.id = cp.preserve_id
    WHERE
        cp.country_id = country_id;
END //

DELIMITER ;

CALL udp_increase_salaries_by_country('Germany');