show DATABASES;

drop database nengdie;

create database nengdie;

show CREATE DATABASE nengdie;

use nengdie;

# can not rename database
# alter nengdie rename nengdie woshinibaba;

# delete a table
drop table user_info;

# create a table
create table user_info (
   user_id TINYINT(3) PRIMARY KEY,
   user_name VARCHAR(30) not null,
   email_address VARCHAR(50),
   age SMALLINT(4) not null,
   gender VARCHAR(5) DEFAULT 'male'
);

# read all tables
show tables;

# read a table
describe user_info;
show create table user_info;

# modify a table

## change table name
alter table user_info rename user_information;
show tables;
alter table nengdie.user_information rename user_info;
show tables;

## add a column
alter table user_info add column favoriteID tinyint after age;
describe user_info;

## change column position
alter table user_info modify favoriteID smallint after gender;

## change column name
alter table user_info change favoriteID fav_id tinyint;

## modify column data format
alter table user_info modify gender varchar(10);

## delete a column
alter table user_info drop fav_id;
alter table user_info add fav_id tinyint after age;

## modify column CONSTRAINTS
alter table user_info modify user_id tinyint auto_increment;

# DML insert records into a table user_info
insert into user_info( nengdie.user_info.user_name, nengdie.user_info.email, nengdie.user_info.age, nengdie.user_info.gender)
values
       ('wangdada','zeaslity@qq.com',15,'male'),
       ('cxc','cxc@163.com',12,'male'),
       ('nengdie','nengdie@qq.com',30,'male'),
       ('hong','hong@qq.com',25,'female'),
       ('zeaslity','zeaslity@qq.com',18,'male'),
       ('zey','zety@qq.com',18,'male'),
       ('die','die@qq.com',15,'male');

SELECT * FROM user_info;

describe user_info;
describe fav_thing;

## 内连接，只输出符合限定条件的内容
select user_name,age,gender from user_info
inner join
    fav_thing as t on user_id = t.fav_user_id
order by age;

## left outer join 左外连接  讲用户的喜好表 fav_thing与user表连接，查看用户对应喜好的事情
select * from  user_info
left join
    fav_thing as t on user_id =t.fav_user_id
order by age;

## 全外连接
select *
from user_info
full join fav_thing;

# 交叉连接
select * from user_info
cross join fav_thing;