当数据库中表的数量比较多时，不利于维护，本文将以此问题进行详细介绍如何维护mysql表，与如何修改mysql表
改变列的数据类型
[sql]
alter table visitor modify nam varchar(30);
追加新列
[sql]
alter table visitor add age int;
alter table visitor add age int first;
alter table visitor add age int after nam;
改变列的位置
[sql]
alter table visitor modify age int after nam;
改变列名 和 类型
[sql]
alter table visitor change birth birthday date;
删除列
[sql]
alter table visitor drop age;
表的复制
[sql]
create table customerh select * from customer;
create table customerg like customer;
insert into customerg select * from customer;
insert into tb1g(no) select bang from tb1;
表的删除
[sql]
drop table if exists customerg;
drop table customerg;