mysql 设置多个字段聚合自增

DROP TEMPORARY TABLE IF EXISTS ttp_firstInvest;
CREATE TEMPORARY TABLE ttp_firstInvest (
    userid varchar(),
    investdate datetime,
    tendermode int,
    amount decimal(, ),
    projecttype int,
    deadline int,
    title varchar(),
    num smallint UNSIGNED AUTO_INCREMENT,
    PRIMARY KEY (userid, num)
  ) ENGINE = MYISAM;