DDL：data definition language
One: Library related operations
1. Library creation
create database tempdb;
2. Library deletion
drop database tempdb;
3. Library modification
- Change character set
alter database fruitdb character set utf8;
4. Library view
- Full library view
show databases;
- Single library information
show create database mydb;
5. Library usage
- Use database
use mydb;
- View the currently used database
select database();
Two: Table related operations
1. Table creation
create table t_user(id int,name varchar(20));
2. Table delete
drop table t_user;
3. Table modification
- Table name change
alter table t_user rename user;
- Field addition
alter table t_user add address varchar(100);
- Field deletion
alter table t_user drop address;
- Field modification [type or length]
alter table t_user modify name varchar(25);
- Field modification【Add primary key or constraint】
alter table t_test change id id int primary key auto_increment;
- Field modification【Add foreign key】
alter table t_user2 add constraint fk_user_deptment foreignkey(deptid) references deptment(deptid);
- Field modification 【Order】
alter table t_user modify name varchar(25) after age;
- Field modification【Replace】
alter table t_user change name new_name varchar(20);
Table view
- Full table view (under a certain database)
show tables;
- Single table information view
show create table t_user;
- Single table structure (field) view
desc t_user;