回顾DDL语言：
show databases;
create database hufei;
use hufei;
create table emp(name varchar(20),age int(10));
show create table emp \G;
alter table emp rename empp;
show create table empp \G;
alter table empp add column height int(10) first;
desc empp;
alter table empp drop column height;
desc empp;
alter table empp modify name varchar(10);
desc empp;
alter table empp change name newname varchar(20);
desc empp;
drop table empp;
DML 对数据库中表记录的操作，主要包括记录的插入（insert）、删除（delete）、改（update）、查（select）
create database hufei;
use hufei;
create table emp(
ename varchar(10),
hiredate date,sal
decimal(10,2),
deptno int(2)
);
create table dept(
deptno int(2),
deptname varchar(10)
);
insert into emp values('zzx','2000-01-01','100',1);
insert into emp values('lisa','2001-01-01','200',3);
insert into emp values('lifei','2020-01-01','300',2);
insert into emp values('yangfei','2011-01-01','2000',2);
insert into dept values(1,'tech');
insert into dept values(2,'sale');
insert into dept values(5,'fin');
select * from emp;
select * from dept;