--创建表
IF OBJECT_ID('Department','U') IS NOT NULL DROP TABLE Department
CREATE TABLE Department
(
DepartmentID smallint IDENTITY(1,1) NOT NULL,
Name NVARCHAR(20) NOT NULL,
GroupName NVARCHAR(20) NOT NULL,
CONSTRAINT PK_Department_DepartmentID PRIMARY KEY(DepartmentID)
);
--插入两条记录
INSERT INTO Department(Name,GroupName) VALUES('A','帅哥');
INSERT INTO Department(Name,GroupName) VALUES('B','美女');
--查询记录
SELECT * FROM Department
result:
A: Insert a new column
ALTER TABLE Department--添加列
ADD DepartmentIDnew smallint NULL
--修改列DepartmentIDnew的值
UPDATE Department SET DepartmentIDnew=DepartmentID
B: delete the primary key column
--删除列需要先删除其约束
ALTER TABLE Department
DROP CONSTRAINT PK_Department_DepartmentID--删除主键
--删除列
ALTER TABLE Department
DROP COLUMN DepartmentID
Results: The primary key column has been deleted
C: adding constraints to the column
--修改列定义
ALTER TABLE Department
ALTER COLUMN DepartmentIDnew smallint NOT NULL
--给列添加约束(这里是增加主键)
ALTER TABLE Department
ADD CONSTRAINT PK_Department_DepartmentIDnew
PRIMARY KEY(DepartmentIDnew)
D: Enable or disable constraints
--添加CHECK约束
ALTER TABLE Department
ADD CONSTRAINT CK_Department_DepartmentID
CHECK(DepartmentIDnew>=1)
--禁用CHECK约束
ALTER TABLE Department
NOCHECK CONSTRAINT CK_DePARTMENT_DepartmentID
--启用CHECK约束
ALTER TABLE Department
CHECK CONSTRAINT CK_Department_DepartmentID