use message_board;

drop table if exists messages;

create table messages(

id int unsigned primary key auto_increment,

content varchar(500) not null,

username char(20) not null,

create_datetime datetime

default current_timestamp not null,

update_datetime timestamp

default current_timestamp not null

on update current_timestamp

);

ALTER TABLE messages

Change user_name username char(20);

select * from messages

where update_datetime > '2019-03-17 03:21:54'

order by update_datetime desc

limit 30

offset 20

;

select id,content,username,

create_datetime,

update_datetime

from messages limit 10 offset 2;

insert into messages(content, username)

values ('hello world, this is first message', 'Jon');

select

id,content,username,update_datetime

from messages

order by create_datetime

limit 3 offset 3;