1創建表和定義數據完整性

1、創建表

use TSQL2012;

if object_id('dbo.Employees','U') is not null
	drop table dbo.Employees;

create table dbo.Employees
(
	empid int not null,
	firstname varchar(30) not null,
	lastname varchar(30) not null,
	hiredate date not null,
	mgrid int null,
	ssn varchar(20) not null,
	salary money not null
);

2、添加主鍵約束

alter table dbo.Employees
	add constraint PK_Employees
	primary key(empid);

3、添加唯一約束

alter table dbo.Employees
	add constraint UNQ_Employees_ssn
	UNIQUE(ssn);

4、添加外鍵約束

在Orders表的empid列上定義一個外鍵約束，指向Employees表中的empid列。

alter table dbo.Orders
	add constraint FK_Orders_Employees
	foreign key(empid)
	references dbo.Employees(empid);

5、添加CHECK約束

alter table dbo.Employees
	add constraint CHK_Employees_salary
	CHECK(salary >0.00);

4、添加默認約束

爲orderts屬性定義默認約束（即訂單的時間戳）

alter table dbo.Orders
	add constraint DFT_Orders_orderts
	default(sysdatetime()) for orderts;