python学习之老男孩python全栈第九期_数据库day004知识点总结 —— MySQL数据库day4

复习：
    1. MySQL：文件管理的软件
    2. 三部分：
        - 服务端
        - SQL语句
        - 客户端
    3. 客户端：
        - MySQL
        - navicat
    4. 授权操作：
        - 用户操作
        - 授权操作
    5. SQL语句
        - 数据库操作
            - 创建数据库要指定字符编码：
                create database xx default charset=utf8;
            - 删除数据库：
                drop database xx;
        
        - 数据表操作
            - 列
                - 数字
                    整数
                    小数
                - 字符串
                - 时间
                    datatime
                - 二进制
            - 其他：引擎、字符编码、起始值
            
            - 主键索引
            - 唯一索引
            - 外键
                - 一对多
                - 一对一
                - 多对多
                
        PS：数据放在硬盘上
        
        - 数据行操作
            - 增
            - 删
            - 改
            - 查
                - in    not in
                - between and
                - limit
                - group by    having
                - order by
                    -desc
                    -asc
                - like '%a'
                - left join xx on 关系
                - inner join
                - 临时表
                    select * from(select * from tb1 where id<10) as B;
                
        PS：笛卡尔积
        a:三条数据  1 2 3
        select * from a as a1,a as a2;
        1 1、1 2、1 3、2 1、2 2、2 3、3 1、3 2、3 3

 

一. 练习题讲解

    1. 去重：distinct    -- 效率不高
        SELECT distinct student.sid,student.sname from score LEFT JOIN student ON score.student_id=student.sid where score.num<60;

二. pymysql模块：
pip3 install pymysql -i https://pypi.douban.com/simple
python模块：对数据库进行操作（SQL语句）

import pymysql

'''
user = input('username:')
pwd = input('possword:')

conn = pymysql.connect(host='localhost', user='root', password='lpg123456', database='db1')     # 打开数据库
cursor = conn.cursor()          # 游标
# 连接数据库成功
sql = "select * from userinfo where username = %(u)s and password = %(p)s "
cursor.execute(sql, {'u': user, 'p': pwd})
result = cursor.fetchone()

cursor.close()
conn.close()

if result:
    print('登录成功')
else:
    print('登录失败')

'''

# 增 删 改

'''
conn = pymysql.connect(host='localhost',user='root',password='lpg123456',database='db1')
cursor = conn.cursor()
sql = "insert into userinfo(username, password) values('egon','123456')"
cursor.execute(sql)

conn.commit()           # 提交  增 删 改  需要用commit

cursor.close()
conn.close()
'''

'''

user = 'wusir'
pwd = '123456'
conn = pymysql.connect(host='localhost',user='root',password='lpg123456',database='db1')
cursor = conn.cursor()
# sql = "insert into userinfo(username, password) values(%s,%s)"
# cursor.execute(sql,[user,pwd])

# 增加多个
sql = "insert into userinfo(username, password) values(%s,%s)"
# r：受影响的行数
r = cursor.executemany(sql,[('laoyao','sb'),('taibai','SB')])       # 只适用于insert


conn.commit()           # 提交  增 删 改  需要用commit

cursor.close()
conn.close()

'''

# 查

'''

conn = pymysql.connect(host='localhost',user='root',password='lpg123456',database='db1')
cursor = conn.cursor(cursor=pymysql.cursors.DictCursor)         # 默认cursor为None，改成以字典形式打印

sql = "select * from userinfo limit 10"
# r：受影响的行数
cursor.execute(sql)

# result = cursor.fetchone()        # 一次取一个
# print(result)
#
# result = cursor.fetchone()
# print(result)
#
# result = cursor.fetchone()
# print(result)

# result = cursor.fetchmany(4)        # 一次取多个
# print(result)

result = cursor.fetchall()          # 一次取所有
print(result)
# [{'id': 1, 'username': 'alex', 'password': '123456'}, {'id': 2, 'username': 'egon', 'password': '123456'}, {'id': 5, 'username': 'wusir', 'password': '123456'}, {'id': 6, 'username': 'laoyao', 'password': 'sb'}, {'id': 7, 'username': 'taibai', 'password': 'SB'}]

cursor.close()
conn.close()

'''


# 新插入数据的自增ID    :cursor.lastrowid

conn = pymysql.connect(host='localhost',user='root',password='lpg123456',database='db1')
cursor = conn.cursor(cursor=pymysql.cursors.DictCursor)
sql = "insert into userinfo(username,password) values('asdsafd','467467')"
cursor.execute(sql)
conn.commit()
print(cursor.lastrowid)

cursor.close()
conn.close()

 

        - 连接、关闭(游标)
        - execute()   --> SQL注入问题
        - 增删改 ： conn.commit()
        - fetchone()
        - fetchmany()
        - fetchall()
        - 获取插入数据的自增ID：lastrowid