MySQL和Python交互的示例

一.准备数据

创建数据表

-- 创建 "京东" 数据库create database jing_dong charset=utf8;-- 使用 "京东" 数据库use jing_dong;-- 创建一个商品goods数据表create table goods( id int unsigned primary key auto_increment not null, name varchar(150) not null, cate_name varchar(40) not null, brand_name varchar(40) not null, price decimal(10,3) not null default 0, is_show bit not null default 1, is_saleoff bit not null default 0);

select name,price from goods where cate_name = '超级本';

select cate_name from goods group by cate_name;

select round(avg(price),2) as avg_price from goods;

select cate_name,avg(price) from goods group by cate_name;

select cate_name,max(price),min(price),avg(price),count(*) from goods group by cate_name;

select id,name,price from goods where price > (select round(avg(price),2) as avg_price from goods) order by price desc;

select * from goodsinner join  (  select  cate_name,   max(price) as max_price,   min(price) as min_price,   avg(price) as avg_price,   count(*) from goods group by cate_name ) as goods_new_info on goods.cate_name=goods_new_info.cate_name and goods.price=goods_new_info.max_price;

select cate_name from goods group by cate_name;

insert into goods_cates (name) select cate_name from goods group by cate_name;

update goods as g inner join goods_cates as c on g.cate_name=c.name set g.cate_name=c.id;

-- select brand_name from goods group by brand_name;-- 在创建数据表的时候一起插入数据-- 注意: 需要对brand_name 用as起别名，否则name字段就没有值create table goods_brands ( id int unsigned primary key auto_increment, name varchar(40) not null) select brand_name as name from goods group by brand_name;

update goods as g inner join goods_brands as b on g.brand_name=b.name set g.brand_name=b.id;

desc goods;

alter table goods change cate_name cate_id int unsigned not null,change brand_name brand_id int unsigned not null;

insert into goods_cates(name) values ('路由器'),('交换机'),('网卡');insert into goods_brands(name) values ('海尔'),('清华同方'),('神舟');

insert into goods (name,cate_id,brand_id,price)values('LaserJet Pro P1606dn 黑白激光打印机', 12, 4,'1849');

select g.id,g.name,c.name,b.name,g.price from goods as ginner join goods_cates as c on g.cate_id=c.idinner join goods_brands as b on g.brand_id=b.id;

select g.id,g.name,c.name,b.name,g.price from goods as gleft join goods_cates as c on g.cate_id=c.idleft join goods_brands as b on g.brand_id=b.id;

-- 需要先获取外键约束名称,该名称系统会自动生成,可以通过查看表创建语句来获取名称show create table goods;-- 获取名称之后就可以根据名称来删除外键约束alter table goods drop foreign key 外键名称;

三.数据库的设计

创建 "商品分类" 表(之前已经创建,无需再次创建)

create table goods_cates( id int unsigned primary key auto_increment not null, name varchar(40) not null);

from pymysql import *

close()关闭连接
commit()提交
cursor()返回Cursor对象，用于执行sql语句并获得结果

Cursor对象

用于执行sql语句，使用频度最高的语句为select、insert、update、delete
获取Cursor对象：调用Connection对象的cursor()方法

cs1=conn.cursor()

close()关闭
execute(operation [, parameters ])执行语句，返回受影响的行数，主要用于执行insert、update、delete语句，也可以执行create、alter、drop等语句
fetchone()执行查询语句时，获取查询结果集的第一个行数据，返回一个元组
fetchall()执行查询时，获取结果集的所有行，一行构成一个元组，再将这些元组装入一个元组返回

对象的属性

rowcount只读属性，表示最近一次execute()执行后受影响的行数
connection获得当前连接对象

五.增删改查

from pymysql import *def main(): # 创建Connection连接 conn = connect(host='localhost',port=3306,database='jing_dong',user='root',password='mysql',charset='utf8') # 获得Cursor对象 cs1 = conn.cursor() # 执行insert语句，并返回受影响的行数：添加一条数据 # 增加 count = cs1.execute('insert into goods_cates(name) values("硬盘")') #打印受影响的行数 print(count) count = cs1.execute('insert into goods_cates(name) values("光盘")') print(count) # # 更新 # count = cs1.execute('update goods_cates set name="机械硬盘" where name="硬盘"') # # 删除 # count = cs1.execute('delete from goods_cates where id=6') # 提交之前的操作，如果之前已经之执行过多次的execute，那么就都进行提交 conn.commit() # 关闭Cursor对象 cs1.close() # 关闭Connection对象 conn.close()if __name__ == '__main__': main()

一.准备数据

创建数据表

三.数据库的设计

创建 "商品分类" 表(之前已经创建,无需再次创建)

Cursor对象

五.增删改查

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