帮我分配项目 [英] Help me bit assignment project

问题描述

我在上学时遇到了一些麻烦。以下是我需要回答的问题。



employee table_zpswtkoqjyh.jpg摄影：dao1001 | Photobucket [ ^ ]



员工表2_zpsrqnsrmhf.jpg摄影：dao1001 | Photobucket [ ^ ]



请帮我解答一下......



谢谢



我尝试过的事情：



我以前用教程在SQLPLUS中创建表但是它对我不起作用。

I have some trouble a bit with an assignment for school. Here are the following questions I need some answer for.

employee table_zpswtkoqjyh.jpg Photo by dao1001 | Photobucket[^]

employee table 2_zpsrqnsrmhf.jpg Photo by dao1001 | Photobucket[^]

Please help me answer a bit...

Thanks

What I have tried:

I used to tutorial create tables in SQLPLUS but it does not work for me.

推荐答案

使用Sql Server Management Studio，它非常简单： cretae表Sql Server Management Studio - Google搜索 [ ^ ]为您提供大量链接，包括视频教程以指导您完成。

Use Sql Server Management Studio and it's pretty simple: cretae table Sql Server Management Studio - Google Search[^] gives you loads of links, including video tutorials to guide you through.

PRIMARY KEY 是一个约束，表示一组列是唯一而不是NULL。大多数实现使用索引来支持这一点，在某些实现中，主键也是用于在磁盘存储中的页面中对数据进行排序的集群索引。



FOREIGN KEY 是一个约束，表示一组列引用另一个表中的另一组列。通常，外键仍然可以为NULL，但如果它不是NULL，则它必须是它引用的表中的有效键，并且也必须是唯一的。它引用的密钥不必是PRIMARY KEY，只是一个唯一的密钥

PRIMARY KEY is a constraint indicates that a set of columns are unique and not NULL. Most implementations use an index to support this and in some implementation the primary key is also the clustering index for ordering the data in pages in disk storage.

FOREIGN KEY is a constraint that indicates that a set of columns refer to another set of columns in another table. Generally a foreign key can still be NULL, but if it is not NULL, then it has to be a valid key in the table it references and that also has to be unique. The key it references DOES NOT have to be the PRIMARY KEY, just a unique key

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