数据定义语言DDL - 建库建表

数据库文件构成：主文件（MDF）、次要文件（NDF）、日志文件（LDF）

其中主文件和日志文件是必须的，次要文件可以有多个（存放在不同分区以提高速度），也可以没有

创建数据库文件主要用到5个属性：

name、filename、size、maxsize、filegrowth

use master
go

if exists (select * from sysdatabases where name=‘db‘)
drop database db
go

create database db
on primary
(
    name = ‘db_mdf‘,
    filename = ‘c:\temp\db.mdf‘,
    size = 10,
    maxsize = 100,
    filegrowth = 5
),
(
    name = ‘db_ndf‘,
    filename = ‘c:\temp\db.ndf‘,
    size = 10,
    maxsize = 100,
    filegrowth = 5
)
log on
(
    name = ‘db_ldf‘,
    filename = ‘c:\temp\db.ldf‘,
    size = 10,
    maxsize = 100,
    filegrowth = 5
)
go

常见数据类型

字符：char、varchar、nvarchar

数值：int、decimal

时间：date、datetime

布尔：bit

图片：image

文本：xml

创建表的SQL语句

use db
go

if exists (select * from sysobjects where name=‘score‘)
drop database score
go

if exists (select * from sysobjects where name=‘corse‘)
drop database corse
go

if exists (select * from sysobjects where name=‘grade‘)
drop database grade
go

if exists (select * from sysobjects where name=‘student‘)
drop database student
go

create table student
(
    id int primary key identity(1,1),
    name nvarchar(50) not null,
    gender bit default ‘true‘,
    joindate date default getdate()
)
go

create table grade
(
    id int primary key identity(1,1),
    name nvarchar(50) not null unique,
    state bit default ‘true‘
)
go

create table corse
(
    id int primary key identity(1,1),
    name nvarchar(50) not null unique,
    state bit default ‘true‘,
    gradeid int not null,
    constraint fk_corse_gradeid foreign key (gradeid) references grade(id)
)
alter table corse nocheck constraint fk_corse_gradeid
go

create table score
(
    studentid int foreign key references student(id) on delete cascade,
    corseid int foreign key references corse(id) on delete cascade,
    examtime datetime default getdate(),
    value decimal(4,1) check(value between 0 and 100),
    constraint pk_score primary key clustered (studentid,corseid)
)
go

数据库完整性主要包括：

实体完整性

域完整性

引用完整性

自定义完整性

数据库约束主要包括：

主键：primary key [clustered]

外键：foreign key references [on delete cascade | nocheck constraint]

唯一：unique

非空：not null

检查：check

默认：default