The fourth module mysql python learning _ integrity constraints

The fourth module mysql python learning _ integrity constraints

 

not null与default

unique

primary key

auto_increment

foreign key

 

 An introduction

Constraints width data type, are optional parameters

Role: to ensure data integrity and consistency
are divided into:

Primary  Key          - the identifier of the field for the table's primary key can uniquely identify a record 
Foreign  Key             - identify the foreign key fields for table 
Not  null             - identifier of the field can not be blank 
UNIQUE  Key              - the value of the identification field is the only 
AUTO_INCREMENT         - value of the identification field of the automatic growth (primary key and an integer type) 
default                 - set the field to the default value 


unsigned             - unsigned 
ZEROFILL             - filled with 0s

 

 

 Two not null and default

 

create table tb11(
id int not null default 2, 
num int  not null 
);

 

 

mysql> desc tb11;
+-------+---------+------+-----+---------+-------+
| Field | Type    | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| id    | int(11) | NO   |     | 2       |       |
| num   | int(11) | NO   |     | NULL    |       |
+-------+---------+------+-----+---------+-------+

 

 

mysql> insert into tb11(num) values(21);
Query OK, 1 row affected (0.00 sec)

mysql> select * from tb11;
+----+-----+
| id | num |
+----+-----+
|  2 |  21 |
+----+-----+

 

 

 

mysql> create table student(
    -> name char(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'
    -> );
Query OK, 0 rows affected (0.04 sec)

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

mysql> select * from student;
+------+-----+------+------------+
| name | age | sex  | hobby      |
+------+-----+------+------------+
| egon |  18 | male | play,music |
+------+-----+------+------------+
1 row in set (0.00 sec)

 

 

 三 unique 

1.设置唯一约束 UNIQUE

 

-- 方法一
create table tt1(
id int,
name char(20) unique,
comment char(20)
);

-- 方法二
create table tt2(
id int,
name char(20),
comment char(20),
unique(name)
);

 

 

 

 

 

create table tt11(
id int not null unique);

等于

create table tt12( 
id int primary key );

 

 

2. Set a unique joint

 

mysql> create table  service(
    -> id int primary key auto_increment,
    -> name  char(20),
    -> host varchar(15) not null,
    -> port int not null,
    -> unique(host,port)
    -> );
Query OK, 0 rows affected (0.03 sec)

mysql> insert into  service values
    -> (1,'nginx','192.168.2.1',80),
    -> (2,'haproxy','192.168.2.2',80),
    -> (3,'mysql','192.168.2.3',3306)
    -> ;
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> insert into  service(name,host,port) values('nginx','192.168.2.1',80);
ERROR 1062 (23000): Duplicate entry '192.168.2.1-80' for key 'host'

 

 

 

 

四 primary key

 

Primary key field value is not null and unique

 

A table can be
single primary key is
multi-column as a primary key (composite primary key)

 

But within a table can have only one primary key primary key

 

1. The primary key is a single column

-   Method a null + UNIQUE Not 
Create  Table TA1 ( 
ID int  Not  null  UNIQUE , 
name VARCHAR ( 20 is ), 
Comment VARCHAR ( 100 ) 
); 

-   Method Two Key Primary 
Create  Table TA2 ( 
ID int  Primary  Key , 
name VARCHAR ( 20 is ), 
Comment VARCHAR ( 100 ) 
); 

- method three defined primary key separately after all fields 

Create  Table ta3(
id int ,
name varchar(20),
comment varchar(100),
primary key(id)
);

 

 

More than two columns as a primary key 

 

 

create table service(
ip varchar(15),
port char(5),
service_name varchar(10) not null,
primary key(ip,port)
);

 

 

 

Five auto_increment

 

Field is automatically constrained growth, constrained key field must be constrained
1. Not specified id, automatically increase
2 to specify ID
3. For the self-energizing field, after deleting a delete, insert the value of the field is still in accordance with position before deleting continue to grow
4. empty tables truncate truncate table tb11;

 

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

 

 

Six foreign key

# 1 , establishing relationships between tables: 
    # first build table is associated, and to ensure that the field is associated with only 
    Create  Table DEP ( 
        ID int  Primary  Key , 
        name char ( 16 ), 
        Comment char ( 50 ) 
    ); 


    # re-association table 
    Create  Table EMP ( 
        ID int  Primary  Key , 
        name char ( 10 ), 
        Sex enum ( ' MALE ' , ' FEMALE ' ),
        the dep_id int ,
         Foreign  Key (the dep_id) References DEP (ID) 
         ON  Delete  Cascade  
        ON  Update  Cascade 
    ); 

# 2 , insert data 
# prior to the association table inserted into the recording 
        INSERT  INTO DEP values 
        ( . 1 , "the IT", "technical capacity limited sector "), 
        ( 2 ," sales "," lack of capacity sales department "), 
        ( 3 ," Finance "," money special multi-sectoral "); 

# Beyond associated table to insert records 
        iNSERT  INTO emp values 
        ( 1 , ' Egon ' ,'male',1);

        insert into emp values
        (2,'alex','male',1),
        (3,'wupeiqi','female',2),
        (4,'yuanhao','male',3),
        (5,'jinximn','male',2);