1.首先创建一客户张表
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.主键约束
-- Primary key
ALTER TABLE dbo.Employees
ADD CONSTRAINT PK_Employees
PRIMARY KEY(empid);
对于主键约束后台将创建一个唯一索引，以物理机制强制逻辑的唯一性约束
3.唯一约束
-- Unique
ALTER TABLE dbo.Employees
ADD CONSTRAINT UNQ_Employees_ssn
UNIQUE(ssn);
4.外键约束 创建一张订单表 插入外键
IF OBJECT_ID('dbo.Orders', 'U') IS NOT NULL
DROP TABLE dbo.Orders;
CREATE TABLE dbo.Orders
(
orderid INT NOT NULL,
empid INT NOT NULL,
custid VARCHAR(10) NOT NULL,
orderts DATETIME2 NOT NULL,
qty INT NOT NULL,
CONSTRAINT PK_Orders
PRIMARY KEY(orderid)
);
-- Foreign keys
ALTER TABLE dbo.Orders
ADD CONSTRAINT FK_Orders_Employees
FOREIGN KEY(empid)
REFERENCES dbo.Employees(empid);
5.CHECK约束
-- Check
ALTER TABLE dbo.Employees
ADD CONSTRAINT CHK_Employees_salary
CHECK(salary > 0.00);
6.默认约束
-- Default
ALTER TABLE dbo.Orders
ADD CONSTRAINT DFT_Orders_orderts
DEFAULT(SYSDATETIME()) FOR orderts;
-- Cleanup
DROP TABLE dbo.Orders, dbo.Employees;