常用sql语句（mysql测试）

DB数据库，Database
DBMS数据库管理系统，DatabaMemanagmentSystem
SQL结构化查询语言，structure Query Language

开启服务
net start mysql80

登录
mysql -u root -p

显示数据库

show databases;

使用数据库
use mysql;

显示数据库表
show tables;
show tables from mysql;

显示数据库
select database();

desc stuinfo;

创建数据库
create database test;

创建数据库表

create table customer(id int,name varchar(20),password varchar(20),email varchar(30));

删除某列

alter table customer drop id;

插入一条数据
insert into stuinfo(id,name) values(1,'John');

查询
select * from stuinfo;

修改
update stuinfo set name='jack' where id=1;

删除字段

alter table songinfo drop id;

删除值
delete from stuinfo where id=1;

插入新字段在...之后（增加字段）

alter table songinfo add id int primary key auto_increment after score;

插入新字段最前面

alter table songinfo add id int primary key auto_increment first;

插入布尔型

alter table post add essence bit;

重置id

alter table news auto_increment=1;

修改字段名

alter table groupcategory change title grouptitle varchar(10);

修改字段类型

alter table t_hp_new modify column thumb blob;

升序/倒序查询

select * from user order by id asc;

select * from user order by id desc;

显示版本
select version();

修改密码

ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'password';

保存图片为二进制数据流

创建表：create table pic_bin(id INT PRIMARY KEY AUTO_INCREMENT,filename VARCHAR(100),data MEDIUMBLOB);

java存储代码

try {
                conn = JdbcUtil.connection();
                String sql1="insert into pic_bin(filename,data) values(?,?)";
                ps = conn.prepareStatement(sql1);
                ps.setObject(1,"a.jpg");

                InputStream in=new FileInputStream("C:\\Users\\Administrator\\Desktop\\test.jpg");
                ps.setObject(2,in);

                ps.execute();
            }catch (Exception e){
                e.printStackTrace();
            }finally {

java读取代码

try {
                conn = JdbcUtil.connection();
                String sql1="select filename,data from pic_bin where id=?";
                ps = conn.prepareStatement(sql1);
                ps.setObject(1,"1");

                rs=ps.executeQuery();

                if(rs.next()){
                    String filename=rs.getString("filename");

                    InputStream in=rs.getBinaryStream("data");

                    OutputStream out=new FileOutputStream("f:\\"+filename);
                    out.write(in.readAllBytes());

                    out.close();
                }