1. #回滚事务
    2. start transaction; #先运行，之后是可以回滚事务的
    4. #如果没有运行 start transaction，那么一旦运行插入数据，将会自动提交，无法回滚
    5. insert into dept_bak(deptno,dname,loc) values (10,'clerk','HUNAN');
    6. insert into dept_bak(deptno,dname,loc) values (10,'clerk','HUNAN');
    7. insert into dept_bak(deptno,dname,loc) values (10,'clerk','HUNAN');
    8. #回滚
    9. rollback;
    11. select * from dept_bak;
    14. #提交事务
    15. start transaction;
    17. insert into dept_bak(deptno,dname,loc) values (20,'SALESMAN','SHANGHAI');
    18. insert into dept_bak(deptno,dname,loc) values (20,'SALESMAN','SHANGHAI');
    19. insert into dept_bak(deptno,dname,loc) values (20,'SALESMAN','SHANGHAI');
    20. insert into dept_bak(deptno,dname,loc) values (20,'SALESMAN','SHANGHAI');
    21. #一旦提交，则无法再回滚
    22. commit;
    24. rollback;