安裝：
初始化        D:\mysql-8.0.12-winx64\mysql-8.0.12-winx64\bin\mysqld --initialize-insecure
運行服務端    D:\mysql-8.0.12-winx64\mysql-8.0.12-winx64\bin\mysqld
運行客戶端    D:\mysql-8.0.12-winx64\mysql-8.0.12-winx64\bin\mysql -u root -p 
            # 查看數據庫 show databases;
            # 創建數據庫 creat database db1;
#
 
 安裝windows服務：
    # C:\Windows\system32>D:\mysql-8.0.12-winx64\mysql-8.0.12-winx64\bin\mysqld --install    [--remove移除]
    # 添加後可以在windows的服務裏看到“MySQL”，管理員身份運行cmd，輸入net start/stop MySQL即可啟動
    
登陸數據庫後創建用戶
    create user ‘username‘@‘ip‘ identified by ‘userpwd‘;
    # ip 填 % 表示所有的ip地址都可登陸
    
為用戶授權
    grant all privileges on db.t to 
 
‘username‘@‘ip‘;
    # all privileges表示除授權權限外擁有所有的權限    也可填select,delete (查權限和刪權限)等
    # db.t 表示對哪個數據庫下的哪個表有此權限，填*.*意味著擁有 所有數據庫下的所有表 的權限
    取消授權：
        revoke update,delete on db.t1 from ‘username‘@‘ip‘;
    
創建數據庫
    create database db2 default charset utf8; # 設置默認編碼
    刪除
        drop database 數據庫名;
    查
        show databases;
    
創建表
    create table t1(id int auto_increment primary key,name char(
 
10))engine=innodb default charset=utf8;
    刪除表
        drop table 表名;
    清空表：
        delete from 表名;        # 自增的id不重置
        truncate table 表名;    # 自增的id重置
        
表的增刪改查
    insert into 表名(列名,列名2) value(列1值,列2值);
    delete from 表名 where 條件;
    update 表名 set 列=值 where 條件;
    select * from 表名;
    
外鍵：
    create table t1(
        uid int auto_increment primary key,
        name varchar(32),
        t2_id int,
        constraint fk_user_userinfo foreign key (t2_id) references userinfo(id)
    )engine=innodb default charset=utf8;
    
    create table t2(
        id int auto_increment primary key,
        sex char(1)
    )engine=innodb default charset=utf8;
innodb原子操作

navicat 鏈接數據庫報錯
# 2059 - Authentication plugin ‘caching_sha2_password‘ cannot be loaded: ......
# use mysql
# select user,host,plugin,authentication_string from user;
# alter user ‘mingyaun‘@‘%‘ identified with mysql_native_password by ‘123456‘;

desc tabl_name;
顯示表結構，字段類型，主鍵，是否為空等屬性，但不顯示外鍵。
show create table table_name;
該命令把創建表的DDL顯示出來，於是表結構、類型，外鍵，備註全部顯示出來了。


關鍵字
- in   not in 
- between and
- limit
- group by  having
- order by 
- like "%a"
- left join xx on  關系
- select * from (select * from tb where id< 10) as B;
- select (select num from score as s2 where s2.student_id=s1.student_id and course_id = 1) as y,from score as s1;
- case when min(num) <10 THEN 0 ELSE min(num) END
- select avg(num),sum(case when num <60 THEN 0 ELSE 1 END) from score GROUP BY course_id order by AVG(num) asc,jgl desc;

import pymysql
# conn = pymysql.connect(host="localhost",user=‘root‘,password=‘‘,database="db666")
# cursor = conn.cursor()
# # sql = "select * from userinfo where username=‘%s‘ and password=‘%s‘" %(user,pwd,)
# # select * from userinfo where username=‘uu‘ or 1=1 -- ‘ and password=‘%s‘
# # ret = cursor.execute(sql)
# # result = cursor.fetchone()
# sql = "select * from userinfo where username=%s and password=%(p)s"
# cursor.execute(sql,user,pwd)
# cursor.execute(sql,[user,pwd])
# cursor.execute(sql,{‘u‘:user,‘p‘:pwd})
# cursor.executemany("insert into hosts(host,color_id)values(%s,%s)", [("1.1.1.11",1),("1.1.1.11",2)])
# conn.commit()    # 增加，刪，改 
# result = cursor.fetchone()
# result = cursor.fetchall()
# result = cursor.fetchmany(4)
# 新插入數據的自增ID: cursor.lastrowid

# cursor.close()
# conn.close()

MySql 基礎 pymysql的基本使用方法