mysql 表完整性約束
阿新 • • 發佈:2019-02-21
ict open let xtra 字符串 none java 財務 oms
約束關鍵字
PRIMARY KEY (PK) 標識該字段為該表的主鍵,可以唯一的標識記錄
FOREIGN KEY (FK) 標識該字段為該表的外鍵
NOT NULL 標識該字段不能為空
UNIQUE KEY (UK) 標識該字段的值是唯一的
AUTO_INCREMENT 標識該字段的值自動增長(整數類型,而且為主鍵)
DEFAULT 為該字段設置默認值
UNSIGNED 無符號
ZEROFILL 使用0填充
not null與default
是否可空,null表示空,非字符串,not null - 不可空,null - 可空;default默認值,創建列時可以指定默認值,當插入數據時如果未主動設置,則自動添加默認值
mysql> create table student( -> name varchar(20) not null, -> age int(2) unsigned not null default 18, -> sex enum(‘male‘,‘female‘) default ‘male‘, -> hobby set(‘play‘,‘study‘,‘read‘,‘music‘) default ‘play,music‘ -> ); mysql> desc student; +-------+------------------------------------+------+-----+------------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+------------------------------------+------+-----+------------+-------+ | name | varchar(20View Code) | NO | | NULL | | | age | int(3) unsigned | NO | | 18 | | | sex | enum(‘male‘,‘female‘) | YES | | male | | | hobby | set(‘play‘,‘study‘,‘read‘,‘music‘) | YES | | play,music | | +-------+------------------------------------+------+-----+------------+-------+ mysql> insert into student(name) values(‘jack‘); mysql> select * from student; +------+-----+------+------------+ | name | age | sex | hobby | +------+-----+------+------------+ | jack | 18 | male | play,music | +------+-----+------+------------+
unique
============設置唯一約束 UNIQUE=============== #方法一: create table department1( id int, name varchar(20) unique, comment varchar(100) ); #方法二: create table department2( id int, name varchar(20), comment varchar(100), constraint uk_name unique(name) ); mysql> insert into department1 values(1,‘IT‘,‘技術‘); Query OK, 1 row affected (0.00 sec) mysql> insert into department1 values(1,‘IT‘,‘技術‘); ERROR 1062 (23000): Duplicate entry ‘IT‘ for key ‘name‘View Code
not null+unique
mysql> create table t1(id int not null unique); Query OK, 0 rows affected (0.02 sec) mysql> desc t1; +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | id | int(11) | NO | PRI | NULL | | +-------+---------+------+-----+---------+-------+ 1 row in set (0.00 sec)
聯合唯一
create table service( id int primary key auto_increment, name varchar(20), host varchar(15) not null, port int not null, unique(host,port) #聯合唯一 ); mysql> insert into service values -> (1,‘nginx‘,‘192.168.0.10‘,80), -> (2,‘haproxy‘,‘192.168.0.20‘,80), -> (3,‘mysql‘,‘192.168.0.30‘,3306) -> ; Query OK, 3 rows affected (0.01 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql> insert into service(name,host,port) values(‘nginx‘,‘192.168.0.10‘,80); ERROR 1062 (23000): Duplicate entry ‘192.168.0.10-80‘ for key ‘host‘View Code
primary key
primary key字段的值不為空且唯一,直接使用not null+unique不就可以了嗎,要它幹什麽?因為主鍵primary key是innodb存儲引擎組織數據的依據,innodb稱之為索引組織表,一張表中必須有且只有一個主鍵。
單列主鍵
============單列做主鍵=============== #方法一:not null+unique create table department1( id int not null unique, #主鍵 name varchar(20) not null unique, comment varchar(100) ); mysql> desc department1; +---------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------+--------------+------+-----+---------+-------+ | id | int(11) | NO | PRI | NULL | | | name | varchar(20) | NO | UNI | NULL | | | comment | varchar(100) | YES | | NULL | | +---------+--------------+------+-----+---------+-------+ rows in set (0.01 sec) #方法二:在某一個字段後用primary key create table department2( id int primary key, #主鍵 name varchar(20), comment varchar(100) ); mysql> desc department2; +---------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------+--------------+------+-----+---------+-------+ | id | int(11) | NO | PRI | NULL | | | name | varchar(20) | YES | | NULL | | | comment | varchar(100) | YES | | NULL | | +---------+--------------+------+-----+---------+-------+ rows in set (0.00 sec) #方法三:在所有字段後單獨定義primary key create table department3( id int, name varchar(20), comment varchar(100), constraint pk_name primary key(id); #創建主鍵並為其命名pk_name mysql> desc department3; +---------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------+--------------+------+-----+---------+-------+ | id | int(11) | NO | PRI | NULL | | | name | varchar(20) | YES | | NULL | | | comment | varchar(100) | YES | | NULL | | +---------+--------------+------+-----+---------+-------+ rows in set (0.01 sec)View Code
多列主鍵
==================多列做主鍵================ create table service( ip varchar(15), port char(5), service_name varchar(10) not null, primary key(ip,port) ); mysql> desc service; +--------------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +--------------+-------------+------+-----+---------+-------+ | ip | varchar(15) | NO | PRI | NULL | | | port | char(5) | NO | PRI | NULL | | | service_name | varchar(10) | NO | | NULL | | +--------------+-------------+------+-----+---------+-------+ 3 rows in set (0.00 sec) mysql> insert into service values -> (‘172.16.45.10‘,‘3306‘,‘mysqld‘), -> (‘172.16.45.11‘,‘3306‘,‘mariadb‘) -> ; Query OK, 2 rows affected (0.00 sec) Records: 2 Duplicates: 0 Warnings: 0 mysql> insert into service values (‘172.16.45.10‘,‘3306‘,‘nginx‘); ERROR 1062 (23000): Duplicate entry ‘172.16.45.10-3306‘ for key ‘PRIMARY‘View Code
auto_increment
約束字段為自動增長,被約束的字段必須同時被key約束
#不指定id,則自動增長 create table student( id int primary key auto_increment, name varchar(20), sex enum(‘male‘,‘female‘) default ‘male‘ ); mysql> desc student; +-------+-----------------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------+-----------------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | name | varchar(20) | YES | | NULL | | | sex | enum(‘male‘,‘female‘) | YES | | male | | +-------+-----------------------+------+-----+---------+----------------+ mysql> insert into student(name) values -> (‘jack‘), -> (‘toms‘) -> ; mysql> select * from student; +----+------+------+ | id | name | sex | +----+------+------+ | 1 | jack | male | | 2 | toms | male | +----+------+------+ #也可以指定id mysql> insert into student values(4,‘lurs‘,‘female‘); Query OK, 1 row affected (0.00 sec) mysql> insert into student values(7,‘rust‘,‘female‘); Query OK, 1 row affected (0.00 sec) mysql> select * from student; +----+------+--------+ | id | name | sex | +----+------+--------+ | 1 | jack | male | | 2 | toms | male | | 4 | lurs | female | | 7 | rust | female | +----+------+--------+ #對於自增的字段,在用delete刪除後,再插入值,該字段仍按照刪除前的位置繼續增長 mysql> delete from student; Query OK, 4 rows affected (0.00 sec) mysql> select * from student; Empty set (0.00 sec) mysql> insert into student(name) values(‘ysb‘); mysql> select * from student; +----+------+------+ | id | name | sex | +----+------+------+ | 8 | ysb | male | +----+------+------+ #應該用truncate清空表,比起delete一條一條地刪除記錄,truncate是直接清空表,在刪除大表時用它 mysql> truncate student; Query OK, 0 rows affected (0.01 sec) mysql> insert into student(name) values(‘jack‘); Query OK, 1 row affected (0.01 sec) mysql> select * from student; +----+------+------+ | id | name | sex | +----+------+------+ | 1 | jack | male | +----+------+------+ 1 row in set (0.00 sec)View Code
foreign key(外鍵約束)
MySQL通過外鍵約束來保證表與表之間的數據的完整性和準確性, 外鍵的使用條件:
- 兩個表必須是InnoDB表,MyISAM表暫時不支持外鍵(據說以後的版本有可能支持,但至少目前不支持);
- 外鍵列必須建立了索引,MySQL 4.1.2以後的版本在建立外鍵時會自動創建索引,但如果在較早的版本則需要顯示建立;
- 外鍵關系的兩個表的列必須是數據類型相似,也就是可以相互轉換類型的列,比如int和tinyint可以,而int和char則不可以;
外鍵定義語法
[CONSTRAINT symbol] FOREIGN KEY [id] (index_col_name, ...) REFERENCES tbl_name (index_col_name, ...) [ON DELETE {RESTRICT | CASCADE | SET NULL | NO ACTION | SET DEFAULT}] [ON UPDATE {RESTRICT | CASCADE | SET NULL | NO ACTION | SET DEFAULT}] 該語法可以在 CREATE TABLE 和 ALTER TABLE 時使用,如果不指定CONSTRAINT symbol,MYSQL會自動生成一個名字。 ON DELETE、ON UPDATE表示事件觸發限制,可設參數: RESTRICT(限制外表中的外鍵改動) CASCADE(跟隨外鍵改動) SET NULL(設空值) SET DEFAULT(設默認值) NO ACTION(無動作,默認的)
簡單示例
#表類型必須是innodb存儲引擎,且被關聯的字段,即references指定的另外一個表的字段,必須保證唯一 create table department( id int primary key, name varchar(20) not null )engine=innodb; #dpt_id外鍵,關聯父表(department主鍵id),同步更新,同步刪除 create table employee( id int primary key, name varchar(20) not null, dpt_id int, constraint fk_name foreign key(dpt_id) references department(id) on delete cascade on update cascade )engine=innodb; #先往父表department中插入記錄 insert into department values (1,‘財務部‘), (2,‘運營部‘), (3,‘銷售部‘); #再往子表employee中插入記錄 insert into employee values (1,‘jack‘,1), (2,‘rusa‘,2), (3,‘susa‘,2), (4,‘toms‘,3), (5,‘qion‘,3), ; #刪父表department,子表employee中對應的記錄跟著刪 mysql> delete from department where id=3; mysql> select * from employee; +----+-------+--------+ | id | name | dpt_id | +----+-------+--------+ | 1 | jack | 1 | | 2 | rusa | 2 | | 3 | susa | 2 | +----+-------+--------+ #更新父表department,子表employee中對應的記錄跟著改 mysql> update department set id=22222 where id=2; mysql> select * from employee; +----+-------+--------+ | id | name | dpt_id | +----+-------+--------+ | 1 | jack | 1 | | 3 | susa | 2 | | 4 | toms | 2 | | 5 | rusa | 2 | +----+-------+--------+
表與表之間常見的關系
#站在左表的角度去找
是否左表的多條記錄可以對應右表的一條記錄,如果是,則證明左表的一個字段foreign key 右表一個字段(通常是id)
#站在右表的角度去找
是否右表的多條記錄可以對應左表的一條記錄,如果是,則證明右表的一個字段foreign key 左表一個字段(通常是id)
#總結:
#多對一:
如果只有步驟1成立,則是左表多對一右表
如果只有步驟2成立,則是右表多對一左表
#多對多
如果步驟1和2同時成立,則證明這兩張表時一個雙向的多對一,即多對多,需要定義一個這兩張表的關系表來專門存放二者的關系
#一對一:
如果1和2都不成立,而是左表的一條記錄唯一對應右表的一條記錄,反之亦然。這種情況很簡單,就是在左表foreign key右表的基礎上,將左表的外鍵字段設置成unique即可
一對多
=========================多對一================= 一對多(或多對一):一個出版社可以出版多本書,關聯方式:foreign key ================================================ create table press( id int primary key auto_increment, name varchar(20) ); create table book( id int primary key auto_increment, name varchar(20), press_id int not null, foreign key(press_id) references press(id) on delete cascade on update cascade ); insert into press(name) values (‘北京工業出版社‘), (‘人民音樂出版社‘), (‘機械工業出版社‘) ; insert into book(name,press_id) values (‘python‘,1), (‘java‘,2), (‘c‘,2), (‘ruby‘,3), (‘c#‘,3) ;View Code
多對多
======================多對多======================= 三張表:出版社,作者信息,書 多對多:一個作者可以寫多本書,一本書也可以有多個作者,雙向的一對多,即多對多 關聯方式:foreign key+一張新的表 =================================================== create table author( id int primary key auto_increment, name varchar(20) ); #這張表就存放作者表與書表的關系,即查詢二者的關系查這表就可以了 create table author_book( id int not null unique auto_increment, author_id int not null, book_id int not null, constraint fk_author foreign key(author_id) references author(id) on delete cascade on update cascade, constraint fk_book foreign key(book_id) references book(id) on delete cascade on update cascade, primary key(author_id,book_id) ); #插入四個作者,id依次排開 insert into author(name) values(‘jack‘),(‘rusa‘),(‘susa‘),(‘toms‘); #每個作者與自己的代表作如下 1 jack: 1 pythom 2 ruby 2 rusa: 1 c# 6 c 3 susa: 4 js 5 html 6 java 4 toms: 3 vb insert into author2book(author_id,book_id) values (1,1), (1,2), (2,1), (2,6), (3,4), (3,5), (3,6), (4,1)View Code
一對一
=======================一對一=============================== 兩張表:學生表和客戶表 一對一:一個學生是一個客戶,一個客戶有可能變成一個學校,即一對一的關系 關聯方式:foreign key+unique 一定是student來foreign key表customer,這樣就保證了: 學生一定是一個客戶, 客戶不一定是學生,但有可能成為一個學生 ============================================================ create table customer( id int primary key auto_increment, name varchar(20) not null, qq varchar(10) not null, phone char(16) not null ); create table student( id int primary key auto_increment, class_name varchar(20) not null, customer_id int unique, #該字段一定要是唯一的 foreign key(customer_id) references customer(id) #外鍵的字段一定要保證unique on delete cascade on update cascade ); #增加客戶 insert into customer(name,qq,phone) values (‘jack‘,‘31811231‘,13811341220), (‘rusa‘,‘123123123‘,15213146809), (‘toms‘,‘283818181‘,1867141331), (‘jiek‘,‘283818181‘,1851143312), (‘alie‘,‘888818181‘,1861243314), (‘heli‘,‘112312312‘,18811431230) ; #增加學生 insert into student(class_name,customer_id) values (‘python‘,3), (‘java‘,4), (‘js‘,5) ;View Code
mysql 表完整性約束