sql基础语法-创建表和约束

USE SQL2016
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,
salary Money Null
);

USE SQL2016
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,
customerid VARCHAR(30) NOT NULL,
qty INT NOT Null,
orderdatetime DATETIME2 NOT NULL,
CONSTRAINT PK_Orders--建立表时，直接创建主键约束
PRIMARY KEY (orderid)
);

--表已经存在，创建主键约束
ALTER TABLE dbo.Employees
ADD CONSTRAINT PK_Employees
PRIMARY KEY(empid);

--唯一约束
ALTER TABLE dbo.Employees 
ADD CONSTRAINT UNQ_Employees_lastname
UNIQUE(lastname);


--外键约束
ALTER TABLE dbo.Orders
ADD CONSTRAINT FK_Orders_Employees
FOREIGN KEY(empid)
REFERENCES dbo.Employees(empid);

--CHECK约束
ALTER TABLE dbo.Employees
Add CONSTRAINT CHK_Employees_Salary
CHECK(salary>0.00);

--默认约束
ALTER TABLE dbo.Orders
ADD CONSTRAINT DFT_Orders_orders
DEFAULT(SYSDATETIME()) FOR orderdatetime

--创建测试数据

--以下两段脚本创建了 两个employee 

USE [SQL2016]
GO

INSERT INTO [dbo].[Employees]
([empid]
,[firstname]
,[lastname]
,[salary])
VALUES
(1,‘zhang‘,‘san‘,5000)
GO

INSERT INTO [dbo].[Employees]
([empid]
,[firstname]
,[lastname]
,[salary])
VALUES
(2,‘li‘,‘si‘,6000)
GO 

--以下脚本创建了两个orders

USE [SQL2016]
GO

INSERT INTO [dbo].[Orders]
([orderid]
,[empid]
,[customerid]
,[qty])
VALUES
(1,1,‘CUS1‘,10)
GO

INSERT INTO [dbo].[Orders]
([orderid]
,[empid]
,[customerid]
,[qty])
VALUES
(2,2,‘CUS2‘,20)
GO

USE [SQL2016]
GO

INSERT INTO [dbo].[Orders]
([orderid]
,[empid]
,[customerid]
,[qty])
VALUES
(3,10,‘CUS1‘,10)
GO

USE [SQL2016]
DELETE FROM dbo.Employees WHERE empid=1
GO

USE [SQL2016]
UPDATE dbo.Employees set empid=4 where empid=1
GO

USE [SQL2016]
GO
UPDATE dbo.Employees set empid=4 where empid=1

DELETE FROM dbo.Employees WHERE empid=2

GO

SELECT * FROM dbo.Orders