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MySQL(三) 完整性約束

ins type ignore select variables 約束 步長 comment set

一.介紹

  約束條件與數據類型的寬度意義,都是可選參數.

  作用:用於保證數據的完整性和一致性.

  主要分為:

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

二.not null與default

  not null 指的時字段的值不可為空,null表示空

  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

技術分享圖片
==================not null====================
mysql> create table t1(id int); #id字段默認可以插入空
mysql> desc t1;
+-------+---------+------+-----+---------+-------+
| Field | Type    | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| id    | int(11) | YES  |     | NULL    |       |
+-------+---------+------+-----+---------+-------+
mysql
> insert into t1 values(); #可以插入空 mysql> create table t2(id int not null); #設置字段id不為空 mysql> desc t2; +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | id | int(11) | NO | | NULL | | +-------+---------+------+-----+---------+-------+ mysql
> insert into t2 values(); #不能插入空 ERROR 1364 (HY000): Field id doesnt have a default value ==================default==================== #設置id字段有默認值後,則無論id字段是null還是not null,都可以插入空,插入空默認填入default指定的默認值 mysql> create table t3(id int default 1); mysql> alter table t3 modify id int not null default 1; ==================綜合練習==================== mysql> create table student( -> name varchar(20) not null, -> age int(3) 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(20) | 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(egon); mysql> select * from student; +------+-----+------+------------+ | name | age | sex | hobby | +------+-----+------+------------+ | egon | 18 | male | play,music | +------+-----+------+------------+
View Code

三.unique

  unique 唯一約束 指該字段的值不能重復

技術分享圖片
============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
使用方法 技術分享圖片
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
聯合唯一

四.primary key

  primary key稱為主鍵約束,用於唯一標識表中的一條記錄.

  從約束角度看primary key字段的值不為空且唯一,那直接制用not null+unique不就可以了嘛,要它幹什麽?

  主鍵primary key時innodb存儲引擎組織數據的依據,innodb稱為索引組織表,一張表中必須有且只有一個主鍵.

  一個表可以有單列做主鍵和多列做主鍵

技術分享圖片
============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)
單列主鍵 技術分享圖片
==================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    |       |
+--------------+-------------+------+-----+---------+-------+
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
多列主鍵

五.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

技術分享圖片
#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
    -> (egon),
    -> (alex)
    -> ;

mysql> select * from student;
+----+------+------+
| id | name | sex  |
+----+------+------+
|  1 | egon | male |
|  2 | alex | male |
+----+------+------+


#也可以指定id
mysql> insert into student values(4,asb,female);
Query OK, 1 row affected (0.00 sec)

mysql> insert into student values(7,wsb,female);
Query OK, 1 row affected (0.00 sec)

mysql> select * from student;
+----+------+--------+
| id | name | sex    |
+----+------+--------+
|  1 | egon | male   |
|  2 | alex | male   |
|  4 | asb  | female |
|  7 | wsb  | 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(egon);
Query OK, 1 row affected (0.01 sec)

mysql> select * from student;
+----+------+------+
| id | name | sex  |
+----+------+------+
|  1 | egon | male |
+----+------+------+
row in set (0.00 sec)
View Code 技術分享圖片
#在創建完表後,修改自增字段的起始值
mysql> create table student(
    -> id int primary key auto_increment,
    -> name varchar(20),
    -> sex enum(male,female) default male
    -> );

mysql> alter table student auto_increment=3;

mysql> show create table student;
.......
ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8

mysql> insert into student(name) values(egon);
Query OK, 1 row affected (0.01 sec)

mysql> select * from student;
+----+------+------+
| id | name | sex  |
+----+------+------+
|  3 | egon | male |
+----+------+------+
row in set (0.00 sec)

mysql> show create table student;
.......
ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8


#也可以創建表時指定auto_increment的初始值,註意初始值的設置為表選項,應該放到括號外
create table student(
id int primary key auto_increment,
name varchar(20),
sex enum(male,female) default male
)auto_increment=3;




#設置步長
sqlserver:自增步長
    基於表級別
    create table t1(
        id int。。。
    )engine=innodb,auto_increment=2 步長=2 default charset=utf8

mysql自增的步長:
    show session variables like auto_inc%;
    
    #基於會話級別
    set session auth_increment_increment=2 #修改會話級別的步長

    #基於全局級別的
    set global auth_increment_increment=2 #修改全局級別的步長(所有會話都生效)


#!!!註意了註意了註意了!!!
If the value of auto_increment_offset is greater than that of auto_increment_increment, the value of auto_increment_offset is ignored. 
翻譯:如果auto_increment_offset的值大於auto_increment_increment的值,則auto_increment_offset的值會被忽略 ,這相當於第一步步子就邁大了,扯著了蛋
比如:設置auto_increment_offset=3,auto_increment_increment=2




mysql> set global auto_increment_increment=5;
Query OK, 0 rows affected (0.00 sec)

mysql> set global auto_increment_offset=3;
Query OK, 0 rows affected (0.00 sec)

mysql> show variables like auto_incre%; #需要退出重新登錄
+--------------------------+-------+
| Variable_name            | Value |
+--------------------------+-------+
| auto_increment_increment | 1     |
| auto_increment_offset    | 1     |
+--------------------------+-------+



create table student(
id int primary key auto_increment,
name varchar(20),
sex enum(male,female) default male
);

mysql> insert into student(name) values(egon1),(egon2),(egon3);
mysql> select * from student;
+----+-------+------+
| id | name  | sex  |
+----+-------+------+
|  3 | egon1 | male |
|  8 | egon2 | male |
| 13 | egon3 | male |
+----+-------+------+
步長:auto_increment_increment,起始偏移量:auto_increment_offset

六.foreign key

  如何找出兩張表之間的關系

分析步驟:
#1、先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)

#2、再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)

#3、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

  建立表之間的關系

#一對多或稱為多對一
三張表:出版社,作者信息,書

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
技術分享圖片
=====================多對一=====================
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
(北京工業地雷出版社),
(人民音樂不好聽出版社),
(知識產權沒有用出版社)
;

insert into book(name,press_id) values
(九陽神功,1),
(九陰真經,2),
(九陰白骨爪,2),
(獨孤九劍,3),
(降龍十巴掌,2),
(葵花寶典,3)
;
View Code

#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
技術分享圖片
=====================多對多=====================
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 author2book(
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(egon),(alex),(yuanhao),(wpq);

#每個作者與自己的代表作如下
egon: 
九陽神功
九陰真經
九陰白骨爪
獨孤九劍
降龍十巴掌
葵花寶典
alex: 
九陽神功
葵花寶典
yuanhao:
獨孤九劍
降龍十巴掌
葵花寶典
wpq:
九陽神功


insert into author2book(author_id,book_id) values
(1,1),
(1,2),
(1,3),
(1,4),
(1,5),
(1,6),
(2,1),
(2,6),
(3,4),
(3,5),
(3,6),
(4,1)
;
View Code

#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
技術分享圖片
#一定是student來foreign key表customer,這樣就保證了:
#1 學生一定是一個客戶,
#2 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
(李飛機,31811231,13811341220),
(王大炮,123123123,15213146809),
(守榴彈,283818181,1867141331),
(吳坦克,283818181,1851143312),
(贏火箭,888818181,1861243314),
(戰地雷,112312312,18811431230)
;


#增加學生
insert into student(class_name,customer_id) values
(脫產3班,3),
(周末19期,4),
(周末19期,5)
;
View Code

級聯操作

  指的是就是同步更新和刪除
  語法:在創建外鍵時 在後面添加 on update cascade 同步更新
                on delete cascade 同步刪除

實例:

技術分享圖片
create table class(id int primary key auto_increment,name char(10));

create table student(
id int primary key auto_increment,
name char(10),
c_id int,
foreign key(c_id) references class(id)
on update cascade
on delete cascade
);

insert into class value(null,"python3期");
insert into student value(null,"羅傲宇",1);
View Code

對主表的id進行更新
以及刪除某條主表記錄 來驗證效果

MySQL(三) 完整性約束