题目内容

在关系R（R#,RN,S#）和S(S#,SN,SD)中，R的主键是R#，S的主键是S#,则S#在R中称为（）

A. 候选码
B. 主键
C. 超码
D. 外键

查看答案

搜索结果不匹配？点我反馈

更多问题

在如下两个数据库表中，若雇员信息表的主键是'雇员号'，部门信息表的主键是'部门号'。雇员信息表中的'部门号'是外键，它参照部门信息表中的'部门号'。若要删除部门信息表中的行，哪一行可以被删除？( )。雇员信息表:雇员号雇员名部门号工资001 黎明 02 2000010 张米 01 1200088 葛晓新 04 1000101 李功诚 02 1500部门信息表:部门号部门名主任01 业务部李建02 销售部吴伟东03 服务部周垠04 财务部包晗

A. 部门号='01'的行
B. 部门号='02'的行
C. 部门号='03'的行
D. 部门号='04'的行

数据库保护分为：安全性控制、、并发性控制和数据恢复。

数据库系统中，实现数据管理功能的核心软件称为。

I Directions: There are ten blanks in the following passage. You are required to fill in each blank with one word or expression selected from the bank of words and expressions given in the box below. You may NOT use any of the words or expressions in the bank more than once. (10 minutes)organizedschedule overwhelmacademiccompromise pressureavailablein other words work outprioritiesperform effectivelyon your own curiosity make it a pointAcademic pressure doesn't necessarily wait until college to become a problem. Over-achieving students who are much younger face burnout（筋疲力尽）, depression and even nervous breakdowns because of the 1) that their parents, schools or they, themselves, place on them to succeed. Here are a few things to do that will help you cope with it.1. Set your 2) and follow them. As the saying goes, “If your destination is unclear, you'll never know if you've arrived.” Make a list of what you need to accomplish and create a 3) for their completion. From time to time, check on your progress. You'll find two things have happened. First, by being 4) , you will most likely be able to accomplish more in less time. Second, you will have a feeling of accomplishment for having done what you have set out to do. Both results will reduce the 5) pressure you may be feeling.2. Start keeping a diary in which you elaborate on（详细描述）the pressures you face. There is nothing so damaging as allowing the pressure to build up within you, because it will inhibit （禁止）your ability to produce. Also, simply putting your feelings on paper tends to reduce the pressure more 6) .3. Make as many friends as you can, and spend time with people you love and who love you. 7) to spend time with them at least once or twice each week. Diversions（转移，分散） such as this tend to keep your mind off of the stress, besides being enjoyable.4. If you still find the academic pressure unbearable, consider professional help. A professional, now is a recognized way to solve this type of problem. Probably you will find such help 8) at your school. If not, seek help 9) .5. Exercise daily. Taking a few minutes to briskly walk around the block can make you more relaxed. If you have more time, 10) at a gym or run a mile. There is nothing that can reduce the feeling of stress more than exercise.