查看多少库存在？
show databases;
建库：
create database yintao;
查看
show databases;
使用库
use yintao;
建表
create table students(
id int unsigned not null auto_increment primary key,
name char(8) not null,
sex char(4) not null,
age tinyint unsigned not null,
tel char(13) null default "-"
);
查看
show tables;
desc students;
增 insert
insert [into] 表名 [(列名1, 列名2, 列名3, ...)] values (值1, 值2, 值3, ...);
insert into students values(NULL, "王刚", "男", 20, "13811371377");
insert into students (name, sex, age) values("孙丽华", "女", 21);
删 delete
delete from 表名称 where 删除条件;
delete from students;
delete from students where id=2;
delete from students where age<20;
改 update
update 表名称 set 列名称=新值 where 更新条件;
update students set tel=default where id=5;
update students set age=age+1;
update students set name="张伟鹏", age=19 where tel="13288097888";
查 select
select 列名称 from 表名称 [查询条件];
select name, age from students;
select * from students;
select * from students where age > 21;
select * from students where name like "%王%";
select * from students where id<5 and age>20;