mybatis的原因!!!!! 数据库这个样子 在postman中调用接口:SQL select * from T_TRAIN_MARSHALLING where TRAIN_NUM is null and PRE_TRAIN_NUMBER is null and RECEIVE_SEND=#{RECEIVE_SEND} union all select * from T_TRAIN_MARSHALLING where TRAIN_NUM = #{TRAIN_NUM} and PRE_TRAIN