在sql語句中注意「約束的概念":
1.實體完整性約束(主鍵--唯一且非空) primary key()
違約處理:no action(拒絕執行)
2.參照完整性約束(外來鍵約束)foregin key() references tablename(filedname) [on delete|update casecade | no action]
違約處理:級聯更新或拒絕執行
3.使用者自定義完整性約束(not null,unique,check短語)
違約處理:拒絕執行
//新增列語法
//【alter table blog_article add columname type constraint】
//新增約束例子
//【alter table blog_article add constraint foreign key(category_name) references blog_category(category_name) on delete cascade on update cascade】
create database blog;
create table blog_user
( user_name char(15) not null check(user_name !=''),
user_password char(15) not null,
user_emial varchar(20) not null unique,
primary key(user_name)
)engine=innodb default charset=utf8 auto_increment=1;
create table blog_category
( category_name char(18) not null check(category_name!=''),
category_date datetime not null,
primary key(category_name)
)engine=innod default charset=utf8 auto_increment=1;
create table blog_article
( article_id int unsigned not null auto_increment,
article_title varchar(20) not null unique,
article_content longtext not null,
article_date datetime not null,
article_readtime int unsigned not null default 0,
user_name char(15) not null,
category_name char(18) not null,
primary key(article_id),
foreign key(user_name) references blog_user(user_name) on delete cascade on update cascade,
foreign key(category_name) references blog_category(category_name) on delete cascade on update cascade
)engine=innodb default charset=utf8 auto_increment=1;
create table blog_comment (
comment_id int(10) unsigned not null auto_increment,
comment_content varchar(90) not null,
comment_date datetime not null,
article_id int(10) unsigned not null,
user_name char(15) not null,
primary key (comment_id),
foreign key(article_id) references blog_article(article_id) on delete cascade on update cascade,
foreign key(user_name) references blog_user(user_name) on delete cascade on update cascade
)engine=innodb default charset=utf8 auto_increment=1;
create table blog_photoalbum
( photoalbum_name char(20) not null check(photoalbum_name!=''),
photoalbum_date datetime not null,
primary key(photoalbum_name)
)engine=innodb default charset=utf8;
create table blog_photograph
( photograph_name varchar(20) not null check(photograph_name!=''),
photograph_date datetime not null,
photoalbum_name char(20) not null,
photourl varchar(90) not null,
foreign key(photoalbum_name) references blog_photoalbum(photoalbum_name) on delete cascade on update cascade
)engine=innodb default charset=utf8;
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