MySQL modify foreign key procedure

modify_fk.sql

DROP PROCEDURE IF EXISTS modify_fk;
DELIMITER $$
CREATE PROCEDURE modify_fk (IN $table TEXT, IN $constraint TEXT, IN $column TEXT, IN $references TEXT)
BEGIN
  SET @st1 = CONCAT_WS(" ",
    "ALTER TABLE", $table,
    "DROP FOREIGN KEY", $constraint);
  PREPARE ncv_st1 FROM @st1;
  EXECUTE ncv_st1;

  SET @st2 = CONCAT_WS(" ",
    "ALTER TABLE", $table, "ADD CONSTRAINT", $constraint,
    "FOREIGN KEY (", $column, ") REFERENCES", $references);
  PREPARE ncv_st2 FROM @st2;
  EXECUTE ncv_st2;

  COMMIT;
END$$
DELIMITER ;