完整性約束

1、介紹

約束條件與數據類型的寬度同樣 , 都死可選參數 

做用 : 用於保證數據的完整性和一致性 

主要分爲 : 

primary key  (pk)   # 標識該字段爲該表的主鍵 , 能夠惟一的標識記錄
foreign key  (fk)    #  標識該字段爲該表的外鍵
not null   # 標識該字段不能爲空
unique key (uk)   #標識該字段的值是惟一的
auto_increment   # 標識該字段的值自動增加 (整數類型 , 並且爲主鍵)
default   # 爲該字段設置默認值


unsugned  #無符號
zerofill  # 使用0填充

 

說明:

# 1. 是否容許爲空 , 默認null , 可設置not null , 字段不容許爲空 , 必須賦值
# 2. 字段是否與默認值 , 缺乏的默認值是null , 若是插入記錄時不給字段賦值 , 此字段使用默認值

sex enum('male','female') not null defaull "male"

# 必須爲正值(無符號)  不容許爲空   默認是20  
age int unsigned not null default 20 

# 3. 是不是key

主鍵  primary key
外鍵  foreign  key
索引  (index,unique...)

 

 

2、not null 與default

是否可空，null表示空，非字符串
not null - 不可空
null - 可空

默認值，建立列時能夠指定默認值，當插入數據時若是未主動設置，則自動添加默認值

 

create table tb1(
    nid int not null defalut 2,
    num int not null 
);

 

驗證1：

mysql> create table t11(id int);# id字段默承認覺得空
Query OK, 0 rows affected (0.05 sec)

mysql> desc t11;
+-------+---------+------+-----+---------+-------+
| Field | Type    | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| id    | int(11) | YES   |          | NULL    |       |
+-------+---------+------+-----+---------+-------+
1 row in set (0.03 sec)
mysql> insert into t11 values(); #給t11表插一個空的值
Query OK, 1 row affected (0.00 sec)

#查詢結果以下
mysql> select * from t11;
+------+
| id   |
+------+
| NULL |
+------+
1 row in set (0.00 sec)

 

驗證2：

# 設置not null , 插入值時不能爲空
mysql> create table t12(id int not null);#設置字段id不爲空
Query OK, 0 rows affected (0.03 sec)

mysql> desc t12;
+-------+---------+------+-----+---------+-------+
| Field | Type    | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| id    | int(11) | NO   |     | NULL    |       |
+-------+---------+------+-----+---------+-------+
1 row in set (0.01 sec)

mysql> insert into t12 values();#不能插入空
ERROR 1364 (HY000): Field 'id' doesn't have a default value

 

驗證3：

#  設置id字段有默認值後，則不管id字段是null仍是not null，均可以插入空，插入空默認填入default指定的默認值

# 第一種狀況
mysql> create table t13(id int default 1);
Query OK, 0 rows affected (0.03 sec)

mysql> desc t13;
+-------+---------+------+-----+---------+-------+
| Field | Type    | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| id    | int(11) | YES  |           | 1              |              |
+-------+---------+------+-----+---------+-------+
1 row in set (0.01 sec)

mysql> insert into t13 values();
Query OK, 1 row affected (0.00 sec)

mysql> select * from t13;
+------+
| id   |
+------+
|    1  |
+------+
1 row in set (0.00 sec)


# 第二種狀況
mysql> create table t14(id int not null default 2);
Query OK, 0 rows affected (0.02 sec)

mysql> desc t14;
+-------+---------+------+-----+---------+-------+
| Field | Type    | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| id    | int(11) | NO      |         | 2               |             |
+-------+---------+------+-----+---------+-------+
1 row in set (0.01 sec)

mysql> select * from t14;
+----+
| id |
+----+
|  2 |
+----+
1 row in set (0.00 sec)

 

小練習：

建立學生表student2，設置每一個字段的約束條件。

mysql> create table student2(
    -> id int not null,
    -> name varchar(50) not null,
    -> age int(3) unsigned not null default 18,
    -> sex enum('male','female') default 'male',
    -> fav set('smoke','drink','tangtou') default 'drink,tangtou'
    -> );
Query OK, 0 rows affected (0.01 sec)

# 只插入了not null約束條件的字段對應的值
mysql> insert into student2(id,name) values(1,'heshun');
Query OK, 1 row affected (0.00 sec)

# 查詢結果以下
mysql> select * from student2;
+----+------+-----+------+---------------+
| id | name | age | sex  | fav           |
+----+------+-----+------+---------------+
|  1 | heshun  |  18 | male | drink,tangtou |
+----+------+-----+------+---------------+
1 row in set (0.00 sec)

 

三、unique

中文翻譯：不一樣的。在mysql中稱爲單列惟一

舉例說明：建立公司部門表（每一個公司都有惟一的一個部門）。

mysql> create table department(
    -> id int,
    -> name char(10)
    -> );
Query OK, 0 rows affected (0.01 sec)

mysql> insert into department values(1,'IT'),(2,'IT');
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from department;
+------+------+
| id   | name |
+------+------+
|    1 | IT   |
|    2 | IT   |
+------+------+
2 rows in set (0.00 sec)
# 發現： 同時插入兩個IT部門也是能夠的，但這是不合理的，因此咱們要設置name字段爲unique 解決這種不合理的現象。

驗證以前重複插入記錄的操做是可行的，可是不符合場景

 

接下來，使用約束條件unique，來對公司部門的字段進行設置。

#第一種建立unique的方式
#例子1：
create table department(
    id int,
    name char(10) unique
);
mysql> insert into department values(1,'it'),(2,'it');
ERROR 1062 (23000): Duplicate entry 'it' for key 'name'

#例子2：
create table department(
    id int unique,
    name char(10) unique
);
insert into department values(1,'it'),(2,'sale');

#第二種建立unique的方式
create table department(
    id int,
    name char(10) ,
    unique(id),
    unique(name)
);
insert into department values(1,'it'),(2,'sale');

聯合惟一：

# 建立services表
mysql> create table services(
    -> id int,
    -> ip char(15),
    -> port int,
    -> unique(id),
    -> unique(ip,port)
    -> );
Query OK, 0 rows affected (0.05 sec)

mysql> desc services;
+-------+----------+------+-----+---------+-------+
| Field | Type      | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| id        | int(11)   | YES   | UNI  | NULL       |             |
| ip        | char(15) | YES   | MUL  | NULL       |             |
| port    | int(11) | YES   |          | NULL       |             |
+-------+----------+------+-----+---------+-------+
3 rows in set (0.01 sec)

#聯合惟一，只要兩列記錄，有一列不一樣，既符合聯合惟一的約束
mysql> insert into services values
    -> (1,'192,168,11,23',80),
    -> (2,'192,168,11,23',81),
    -> (3,'192,168,11,25',80);
Query OK, 3 rows affected (0.01 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> select * from services;
+------+---------------+------+
| id   | ip            | port |
+------+---------------+------+
|    1 | 192,168,11,23 |   80 |
|    2 | 192,168,11,23 |   81 |
|    3 | 192,168,11,25 |   80 |
+------+---------------+------+
3 rows in set (0.00 sec)

mysql> insert into services values (4,'192,168,11,23',80);
ERROR 1062 (23000): Duplicate entry '192,168,11,23-80' for key 'ip'

 

4.primary key

一個表中能夠：

單列作主鍵
多列作主鍵（複合主鍵）

約束：等價於 not null unique,字段的值不爲空且惟一

存儲引擎默認是（innodb）:對於innodb存儲引擎來講，一張表必須有一個主鍵。

 

單列主鍵

# 建立t14表，爲id字段設置主鍵，惟一的不一樣的記錄
create table t14(
    id int primary key,
    name char(16)
);

insert into t14 values
(1,'xiaoma'),
(2,'xiaohong');

mysql> insert into t14 values(2,'wxxx');
ERROR 1062 (23000): Duplicate entry '6' for key 'PRIMARY'


#   not null + unique的化學反應，至關於給id設置primary key
create table t15(
    id int not null unique,
    name char(16)
);
mysql> create table t15(
    -> id int not null unique,
    -> name char(16)
    -> );
Query OK, 0 rows affected (0.01 sec)

mysql> desc t15;
+-------+----------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| id        | int(11)  | NO     | PRI | NULL       |             |
| name   | char(16) | YES  |         | NULL       |             |
+-------+----------+------+-----+---------+-------+
2 rows in set (0.02 sec)

複合主鍵

create table t16(
    ip char(15),
    port int,
    primary key(ip,port)
);

insert into t16 values
('1.1.1.2',80),
('1.1.1.2',81);

驗證複合主鍵的使用

5.auto_increment

約束:約束的字段爲自動增加，約束的字段必須同時被key約束

(重點)  驗證 : 

不指定id自動增加

# 建立student
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    |                |
+-------+-----------------------+------+-----+---------+----------------+
3 rows in set (0.17 sec)

#插入記錄
mysql>  insert into student(name) values ('老白'),('小白');
Query OK, 2 rows affected (0.01 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from student;
+----+--------+------+
| id | name   | sex  |
+----+--------+------+
|  1 | 老白   | male |
|  2 | 小白   | male |
+----+--------+------+
2 rows in set (0.00 sec)

 

也能夠指定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 (0.01 sec)

mysql> select * from student;
+----+--------+--------+
| id | name   | sex    |
+----+--------+--------+
|  1 | 老白   | male   |
|  2 | 小白   | male   |
|  4 | asb    | female |
|  7 | wsb    | female |
+----+--------+--------+
4 rows in set (0.00 sec)

# 再次插入一條不指定id的記錄，會在以前的最後一條記錄繼續增加
mysql>  insert into student(name) values ('大白');
Query OK, 1 row affected (0.00 sec)

mysql> select * from student;
+----+--------+--------+
| id | name   | sex    |
+----+--------+--------+
|  1 | 老白   | male   |
|  2 | 小白   | male   |
|  4 | asb    | female |
|  7 | wsb    | female |
|  8 | 大白   | male   |
+----+--------+--------+
5 rows in set (0.00 sec)

對於自增加字段 ,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加

mysql> delete from student;
Query OK, 5 rows affected (0.00 sec)

mysql> select * from student;
Empty set (0.00 sec)

mysql> select * from student;
Empty set (0.00 sec)

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

mysql> select * from student;
+----+------+------+
| id | name | sex  |
+----+------+------+
|  9 | ysb  | male |
+----+------+------+
1 row in set (0.00 sec)

#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 (0.03 sec)

mysql>  insert into student(name) values('xiaobai');
Query OK, 1 row affected (0.00 sec)

mysql> select * from student;
+----+---------+------+
| id | name    | sex  |
+----+---------+------+
|  1 | xiaobai | male |
+----+---------+------+
1 row in set (0.00 sec)

 

瞭解 : 設置步長增長

查看可用的 開頭auto_inc的詞
mysql> show variables like 'auto_inc%';
+--------------------------+-------+
| Variable_name            | Value |
+--------------------------+-------+
| auto_increment_increment | 1     |
| auto_increment_offset    | 1     |
+--------------------------+-------+
2 rows in set (0.02 sec)
# 步長auto_increment_increment,默認爲1
# 起始的偏移量auto_increment_offset, 默認是1

 # 設置步長 爲會話設置，只在本次鏈接中有效
 set session auto_increment_increment=5;

 #全局設置步長 都有效。
 set global auto_increment_increment=5;

 # 設置起始偏移量
 set global  auto_increment_offset=3;

#強調：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：若是auto_increment_offset的值大於auto_increment_increment的值，則auto_increment_offset的值會被忽略 

# 設置完起始偏移量和步長以後，再次執行show variables like'auto_inc%';
發現跟以前同樣，必須先exit,再登陸纔有效。

mysql> show variables like'auto_inc%';
+--------------------------+-------+
| Variable_name            | Value |
+--------------------------+-------+
| auto_increment_increment | 5     |
| auto_increment_offset    | 3     |
+--------------------------+-------+
2 rows in set (0.00 sec)

#由於以前有一條記錄id=1
mysql> select * from student;
+----+---------+------+
| id | name    | sex  |
+----+---------+------+
|  1 | xiaobai | male |
+----+---------+------+
1 row in set (0.00 sec)
# 下次插入的時候，從起始位置3開始，每次插入記錄id+5
mysql> insert into student(name) values('ma1'),('ma2'),('ma3');
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> select * from student;
+----+---------+------+
| id | name    | sex  |
+----+---------+------+
|  1 | xiaobai | male |
|  3 | ma1     | male |
|  8 | ma2     | male |
| 13 | ma3     | male |
+----+---------+------+

auto_increment_increment和 auto_increment_offset

清空表區分delete和truncate的區別：

delete from t1  ; # 若是有自增id 新增的數據, 仍然是以刪除前的最後一個做爲起始 

truncate table t1 ; 數據量大 , 刪除速度比上一條塊 , 且直接從零開始 . 

 

6.foreign key

一 快速理解foreign key

以前建立表的時候都是在一張表中添加記錄，好比以下表：

 

 

 

 

 

司有3個部門，可是有1個億的員工，那意味着部門這個字段須要重複存儲，部門名字越長，越浪費。

這個時候，

解決方法：

咱們徹底能夠定義一個部門表

而後讓員工信息表關聯該表，如何關聯，即foreign key

咱們能夠將上表改成以下結構：

 

 

 

 

 

 

此時有兩張表，一張是employee表,簡稱emp表（關聯表，也就從表）。一張是department表，簡稱dep表（被關聯表，也叫主表）。

 

建立兩張表的操做:

#1.建立表時先建立被關聯表，再建立關聯表
# 先建立被關聯表（dep表）
create table dep(
    id int primary key,
    name varchar(20) not null,
    descripe varchar(20) not null
);

#再建立關聯表（emp表）
create table emp(
    id int primary key,
    name varchar(20) not null,
    age int not null,
    dep_id int,
    constraint fk_dep foreign key(dep_id) references dep(id) 
);

#2.插入記錄時，先往被關聯表中插入記錄，再往關聯表中插入記錄

insert into dep values
(1,'IT','IT技術有限部門'),
(2,'銷售部','銷售部門'),
(3,'財務部','花錢太多部門');

insert into emp values
(1,'zhangsan',18,1),
(2,'lisi',19,1),
(3,'egon',20,2),
(4,'yuanhao',40,3),
(5,'alex',18,2);

3.刪除表
#按道理來講，刪除了部門表中的某個部門，員工表的有關聯的記錄相繼刪除。
mysql> delete from dep where id=3;
ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails (`db5`.`emp`, CONSTRAINT `fk_name` FOREIGN KEY (`dep_id`) REFERENCES `dep` (`id`))

#可是先刪除員工表的記錄以後，再刪除當前部門就沒有任何問題

mysql> delete from emp where dep =3;
Query OK, 1 row affected (0.00 sec)

mysql> select * from emp;
+----+----------+-----+--------+
| id | name     | age | dep_id |
+----+----------+-----+--------+
|  1 | zhangsan |  18 |      1 |
|  2 | lisi     |  18 |      1 |
|  3 | egon     |  20 |      2 |
|  5 | alex     |  18 |      2 |
+----+----------+-----+--------+
4 rows in set (0.00 sec)

mysql> delete from dep where id=3;
Query OK, 1 row affected (0.00 sec)

mysql> select * from dep;
+----+-----------+----------------------+
| id | name      | descripe             |
+----+-----------+----------------------+
|  1 | IT        | IT技術有限部門       |
|  2 | 銷售部    | 銷售部門             |
+----+-----------+----------------------+
2 rows in set (0.00 sec)

上面的刪除表記錄的操做比較繁瑣，按道理講，裁掉一個部門，該部門的員工也會被裁掉。其實呢，在建表的時候還有個很重要的內容，叫同步刪除，同步更新

接下來將剛建好的兩張表所有刪除，先刪除關聯表（emp）,再刪除被關聯表（dep）

接下來：
重複上面的操做建表
注意：在關聯表中加入

on delete cascade  #同步刪除

on update cascade  #同步更新 

 

修改emp 表

create table emp(
    id int primary key,
    name varchar(20) not null,
    age int not null,
    dep_id int,
    constraint fk_dep foreign key(dep_id) references dep(id) 
    on delete cascade #同步刪除
    on update cascade #同步更新
);

 

接下來的操做，就複合咱們正常的生活中的狀況了。

#再去刪被關聯表(dep)的記錄，關聯表(emp)中的記錄也跟着刪除
mysql> delete from dep where id=3;
Query OK, 1 row affected (0.00 sec)

mysql> select * from dep;
+----+-----------+----------------------+
| id | name      | descripe             |
+----+-----------+----------------------+
|  1 | IT        | IT技術有限部門       |
|  2 | 銷售部    | 銷售部門             |
+----+-----------+----------------------+
2 rows in set (0.00 sec)

mysql> select * from emp;
+----+----------+-----+--------+
| id | name     | age | dep_id |
+----+----------+-----+--------+
|  1 | zhangsan |  18 |      1 |
|  2 | lisi     |  19 |      1 |
|  3 | egon     |  20 |      2 |
|  5 | alex     |  18 |      2 |
+----+----------+-----+--------+
4 rows in set (0.00 sec)

#再去更改被關聯表(dep)的記錄，關聯表(emp)中的記錄也跟着更改

mysql> update dep set id=222 where id=2;
Query OK, 1 row affected (0.02 sec)
Rows matched: 1  Changed: 1  Warnings: 0

# 趕忙去查看一下兩張表是否都被刪除了，是否都被更改了
mysql> select * from dep;
+-----+-----------+----------------------+
| id  | name      | descripe             |
+-----+-----------+----------------------+
|   1 | IT        | IT技術有限部門       |
| 222 | 銷售部    | 銷售部門             |
+-----+-----------+----------------------+
2 rows in set (0.00 sec)

mysql> select * from emp;
+----+----------+-----+--------+
| id | name     | age | dep_id |
+----+----------+-----+--------+
|  1 | zhangsan |  18 |      1 |
|  2 | lisi     |  19 |      1 |
|  3 | egon     |  20 |    222 |
|  5 | alex     |  18 |    222 |
+----+----------+-----+--------+
4 rows in set (0.00 sec)