SELECT
    W,
    M
FROM
    (
        SELECT
            A.W,
            T_B.RID,
            CASE    T_B.RID
                WHEN 1 THEN @MOD_M := REPLACE(A.M, T_B.W, T_B.M)
                ELSE @MOD_M := REPLACE(@MOD_M, T_B.W, T_B.M)
            END AS M
        FROM
            A,
            (
                SELECT
                    @ROWNUM := @ROWNUM + 1 AS RID,
                    W,
                    M
                FROM
                    B,
                    (
                        SELECT
                            @ROWNUM := 0
                    ) R
            ) T_B,
            (
                SELECT
                    @MOD_M := ''
            ) T_C
        ) T_D,
        (
            SELECT
                COUNT(1) AS MAX_RID
            FROM
                B
        ) T_E
WHERE
    T_D.RID = T_E.MAX_RID