数据库必须拥有至少几个控制文件（）

单项选择题显示本月月末的日期（）

A.select last_date(sysdate) from dual;
B.select finally_day(sysdate) from dual;
C.select last_day(sysdate) from dual;
D.select tail_day(sysdate) from dual;

单项选择题如何显示今天是星期几（周一到周日，分别用1~7表示）（）

A.select to_char(sysdate,'D') from dual;
B.select to_char(sysdate,'W') from dual;
C.select to_char(sysdate,'D')-1 from dual;
D.select to_char(sysdate-1,'D') from dual;
E.select to_char(sysdate-1,'W') from dual;

单项选择题查询出EMP表中1982年及以后入职的员工信息（）（注：字段hiredate为入职日期，数据类型为DATE型）

A.select * from emp where hiredate>='19820101';
B.select * from emp where hiredate>=to_char('19820101','YYYYMMDD');
C.select * from emp where to_date(hiredate,'YYYYMMDD')>='19820101';
D.select * from emp where to_char(hiredate,'YYYYMMDD')>='19820101';

单项选择题查询出EMP表中COMM字段为空的记录（）

A.select * from emp where comm='';
B.select * from emp where comm=null;
C.select * from emp where nvl(comm)=0;
D.select * from emp where comm is null;
E.select * from emp where nvl(comm,0)=0;

单项选择题取出工资在2000到3000元（包括上下限）之间的员工（）

A.select * from emp wher sal in (2000,3000);
B.select * from emp wher sal like (2000,3000);
C.select * from emp wher sal = (2000,3000);
D.select * from emp wher sal between 2000 and 3000;