Mysql key addition, replicate tables, columns and operations

1. Foreign Key: association relationship between the table (the primary table) (from the table) is associated with the table

2. The three kinds of correspondence relationship between foreign key: many, one-many

3. The rules of grammar and

   

And grammar rules:

Foreign key: Syntax: foreign key (relationship table of the current foreign key field) references are associated with the table name (id) 
Rules: Create principle: create the associated table (the primary table), creating the associated table (the table); remove updates principle (no cascade delete): delete, update data associated with the associated table, then delete the associated data table in the 
cascade delete: delete limit in order to solve the problem: delete the associated table (the primary table) the relationship can be deleted even associated table data (from table) 
cascade syntax: when you create a foreign key in the related table plus   on update cascade on delete cascade

dep_id int not null,
foreign key(dep_id) references dep2(id)
on update cascade
on delete cascade

View Code

AUTO_INCREMENT: from zero by default, may be worth the time to write, writing the initial value is then incremented 
to-many: two table is associated (the primary table) by an association table (Table) to achieve foreign key association of two tables 
many: association table (the table) are related by a foreign key to the association table (the primary table) is not the only foreign keys 
one: association table (the table) by the foreign key is associated with a unique decorrelation table (the primary table) foreign key unique application: a table field division table using too much, with examples

Many examples:

Create a table
         # was associated table: 
            dep2:
                create table dep2(
                    id int primary key auto_increment,
                    dep_name varchar(16),
                    dep_desc varchar(255)
                );

        # Association table: 
            EMP2:
                create table emp2(
                    id int primary key auto_increment,
                    name varchar(16),
                    age int,
                    gender enum('male', 'female', 'others') default 'male',
                    dep_id int not null,
                    foreign key(dep_id) references dep2(id)
                    on update cascade
                    on delete cascade
                );

One example: 

One:
         - one relationship between the two, will be a large amount of data tables, split into two tables.
            - user_info:
                id, name, age, gender, hobby, id_card

            - user:
                id , name, age, detail_id（外键）

            - detail:
                id, gender, hobby, id_card

            user with the detail table to establish a one to one foreign key relationships.
            foreign key should be built at a higher frequency side.

        - Create a table
             # was linked table () 
            the Create the Table the Customer (
                id int primary key auto_increment,
                name varchar(16),
                media varchar(32)
            );


            # Association table (Table) 
            Create Table Student (
                id int primary key auto_increment,
                addr varchar(255),
                phone char(11),
                id_card char(18),

                # Foreign key must be set to a unique 
                customer_id int unique,
                foreign key(customer_id) references customer(id)
                on update cascade
                on delete cascade
            );

 

Many to many: the use of the third table to build two tables-many foreign key relationship

- book:
            create table book(
                    id int primary key auto_increment,
                    title varchar(20),
                    price int,
                    book_content varchar(255)
            );

        - author:
            create table author(
                    id int primary key auto_increment,
                    name varchar(16),
                    age int
            );


        - book2author:
            create table book2author(
                id int primary key auto_increment,
                book_id int,
                author_id int,
                foreign key(book_id) references book(id)
                on update cascade
                on delete cascade,
                foreign key(author_id) references author(id)
                on update cascade
                on delete cascade
            );

 

4. Modify the operating table

Modifying operation table and column renaming

Table 5. Replication

The copy operation table:
        + Record copy table structure (key will not be copied: primary keys, foreign keys and indexes)
        mysql> create table new_service select * from service;

        Just copy the table structure
        # The select * from service where 1 = 2 ; ---> not real data, a table structure 
        MySQL> Create Table new_customer SELECT * from Customer WHERE. 1 = 2;