case1:
ALTER TABLE `mydb`.`cd00_feihu` CHANGE `t1` `t1` TIMESTAMP DEFAULT NULL NULL;
case2:
ALTER TABLE `mydb`.`cd00_feihu` CHANGE `t1` `t1` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP;
case1:
ALTER TABLE `mydb`.`cd00_feihu` CHANGE `t1` `t1` TIMESTAMP DEFAULT NULL NULL;
case2:
ALTER TABLE `mydb`.`cd00_feihu` CHANGE `t1` `t1` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP;