原文：http://blog.csdn.net/qq_33733970/article/details/77799068
show create table \G
alter table userinfo auto_increment=20
desc userinfo：拿到表的描述信息如下
show session variables like ‘auto_in%’
set session auto_increment_increment=2;
show global variables like ‘auto_incre%’;
set global auto_increment_increment=20;