alter user scott account unlock;
时间比较方式：
select * from emp where to_char(hiredate,'yyyy-mm-dd'')>'1982-01-01';
select * from emp where to_char(hiredate,'yyyy')='1980';
select * from emp where to_char(hiredate,'mm')='05';
select name, sal*13+nvl(comm,0)*13 年薪 from emp order by 年薪 desc;