Python——连接数据库操作

一、数据库基础用法

要先配置环境变量，然后cmd安装：pip install pymysql

1、连接MySQL，并创建wzg库

#引入decimal模块
import pymysql#连接数据库
db=pymysql.connect(host='localhost',user='root',password='1234',charset='utf8')#创建一个游标对象（相当于指针）
cursor=db.cursor()#执行创建数据库语句
cursor.execute('create schema wzg default charset=utf8;')
cursor.execute('show databases;')#fetchone获取一条数据（元组类型）
print(cursor.fetchone())
#现在指针到了[1]的位置#fetchall获取全部数据（字符串类型）
all=cursor.fetchall()
for i in all:print(i[0])#关闭游标和数据库连接
cursor.close()
db.close()

2、创建student表，并插入数据

import pymysql#连接数据库，并打开wzg数据库（数据库已创建）
db=pymysql.connect(host='localhost',user='root',password='1234',charset='utf8',db='wzg')#创建游标对象
cursor=db.cursor()try:#创建student表，并执行sql='''create table student(SNO char(10),SNAME varchar(20) NOT NULL,SSEX varchar(1),primary key(SNO))default charset=utf8;'''cursor.execute(sql)#插入一条数据，并执行insert_sql='''insert into student values('200303016','王智刚','男'),('20030001','小明','男')'''cursor.execute(insert_sql)#将数据提交给数据库（加入数据，修改数据要先提交）db.commit()#执行查询语句cursor.execute('select * from student')#打印全部数据all=cursor.fetchall()for i in all:print(i)#发生错误时，打印报错原因
except Exception as e:print(e)#无论是否报错都执行
finally:cursor.close()db.close()

数据库中char和varchar的区别：

char类型的长度是固定的，varchar的长度是可变的。

例如：存储字符串'abc'，使用char(10)，表示存储的字符将占10个字节（包括7个空字符），

使用varchar(10)，表示只占3个字节，10是最大值，当存储的字符小于10时，按照实际的长度存储。

二、项目：银行管理系统

完成功能：1.查询 2.取钱 3.存钱 4.退出

练习：创建信息表，并进行匹配

1、创建数据库为(bank)，账户信息表为(account)

account_id(varchar(20))	Account_passwd(char(6))	Money(decimal(10,2))
001	123456	1000.00
002	456789	5000.00

2、拓展：进行账号和密码的匹配

请输入账号：001

请输入密码：123456

select * from account where account_id=001 and Account_passwd=123456

if cursor.fetchall():

登录成功

else:

登录失败

import pymysql# 连接数据库
db = pymysql.connect(host='localhost', user='root', password='1234', charset='utf8')
cursor = db.cursor()# 创建bank库
cursor.execute('create database bank charset utf8;')
cursor.execute('use bank;')try:# # 创建表# sql = '''create table account(#    account_id varchar(20) NOT NULL,#    account_passwd char(6) NOT NULL,#    money decimal(10,2),#    primary key(account_id)#    );'''# cursor.execute(sql)# # 插入数据# insert_sql = '''# insert into account values('001','123456',1000.00),('002','456789',5000.00)# '''# cursor.execute(insert_sql)# db.commit()# # 查询所有数据# cursor.execute('select * from account')# all = cursor.fetchall()# for i in all:#     print(i)# 输入账号和密码z=input("请输入账号：")m=input("请输入密码：")# 从account表中进行账号和密码的匹配cursor.execute('select * from account where account_id=%s and account_passwd=%s',(z,m))# 如果找到，则登录成功if cursor.fetchall():print('登录成功')else:print('登录失败')except Exception as e:print(e)finally:cursor.close()db.close()

1、进行初始化操作

import pymysql# 创建bank库
CREATE_SCHEMA_SQL='''create schema bank charset utf8;'''# 创建account表
CREATE_TABLE_SQL = '''create table account(account_id varchar(20) NOT NULL,account_passwd char(6) NOT NULL,# decimal用于保存精确数字的类型，decimal(10,2)表示总位数最大为12位，其中整数10位，小数2位money decimal(10,2),primary key(account_id)) default charset=utf8;'''# 创建银行账户
CREATE_ACCOUNT_SQL = '''insert into account values('001','123456',1000.00),('002','456789',5000.00);'''# 初始化
def init():try:DB = pymysql.connect(host='localhost',user='root',password='1234',charset='utf8')cursor1 = DB.cursor()cursor1.execute(CREATE_SCHEMA_SQL)DB = pymysql.connect(host='localhost',user='root',password='1234',charset='utf8',database='bank')cursor2 = DB.cursor()cursor2.execute(CREATE_TABLE_SQL)cursor2.execute(CREATE_ACCOUNT_SQL)DB.commit()print('初始化成功')except Exception as e:print('初始化失败',e)finally:cursor1.close()cursor2.close()DB.close()  # 不让别人调用
if __name__ == "__main__":init()

2、登录检查，并选择操作

import pymysql# 定义全局变量为空
DB=None# 创建Account类
class Account():# 传入参数def __init__(self,account_id,account_passwd):self.account_id=account_idself.account_passwd=account_passwd# 登录检查def check_account(self):cursor=DB.cursor()try:# 把输入账号和密码进行匹配（函数体内部传入参数用self.）SQL="select * from account where account_id=%s and account_passwd=%s" %(self.account_id,self.account_passwd)cursor.execute(SQL)# 匹配成功返回True，失败返回Falseif cursor.fetchall():return Trueelse:return Falseexcept Exception as e:print("错误原因：",e)finally:cursor.close()# 查询余额# def query_money# 取钱# def reduce_money# 存钱# def add_moneydef main():# 定义全局变量global DB# 连接bank库DB=pymysql.connect(host="localhost",user="root",passwd="1234",database="bank")cursor=DB.cursor()# 输入账号和密码from_account_id=input("请输入账号：")from_account_passwd=input("请输入密码：")# 输入的参数传入给Account类，并创建account对象account=Account(from_account_id,from_account_passwd)# 调用check_account方法，进行登录检查if account.check_account():choose=input("请输入操作：\n1、查询余额\n2、取钱\n3、存钱\n4、取卡\n")# 当输入不等于4的时候执行，等于4则退出while choose!="4":# 查询if choose=="1":print("111")# 取钱elif choose=="2":print("222")# 存钱elif choose=="3":print("333")# 上面操作完成之后，继续输入其他操作choose = input("请输入操作：\n1、查询余额\n2、取钱\n3、存钱\n4、取卡\n")else:print("谢谢使用！")else:print("账号或密码错误")DB.close()
main()

3、加入查询功能

存在银行里的钱可能会产生利息，所以需要考虑余额为小数的问题，需要用到decimal库

import pymysql
# 引入decimal模块
import decimal
DB=None
class Account():def __init__(self,account_id,account_passwd):self.account_id=account_idself.account_passwd=account_passwd# 登录检查def check_account(self):cursor=DB.cursor()try:SQL="select * from account where account_id=%s and account_passwd=%s" %(self.account_id,self.account_passwd)cursor.execute(SQL)if cursor.fetchall():return Trueelse:return Falseexcept Exception as e:print("错误",e)finally:cursor.close()# 查询余额def query_money(self):cursor=DB.cursor()try:# 匹配账号密码，并返回moneySQL="select money from account where account_id=%s and account_passwd=%s" %(self.account_id,self.account_passwd)cursor.execute(SQL)money=cursor.fetchone()[0]# 如果账户有钱就返回金额，没钱返回0.00if money:# 返回值为decimal类型，quantize函数进行四舍五入，'0.00'表示保留两位小数return str(money.quantize(decimal.Decimal('0.00')))else:return 0.00except Exception as e:print("错误原因",e)finally:cursor.close()def main():global DBDB=pymysql.connect(host="localhost",user="root",passwd="1234",charset="utf8",database="bank")cursor=DB.cursor()from_account_id=input("请输入账号：")from_account_passwd=input("请输入密码：")account=Account(from_account_id,from_account_passwd)if account.check_account():choose=input("请输入操作：\n1、查询余额\n2、取钱\n3、存钱\n4、取卡\n")while choose!="4":# 查询if choose=="1":# 调用query_money方法print("您的余额是%s元" % account.query_money())# 取钱elif choose=="2":print("222")# 存钱elif choose=="3":print("333")choose = input("请输入操作：\n1、查询余额\n2、取钱\n3、存钱\n4、取卡\n")else:print("谢谢使用")else:print("账号或密码错误")DB.close()
main()

4、加入取钱功能

取钱存钱要用update来执行数据库，还要注意取钱需要考虑 余额是否充足 的问题

import pymysql
import decimal
DB=None
class Account():def __init__(self,account_id,account_passwd):self.account_id=account_idself.account_passwd=account_passwd# 登录检查def check_account(self):cursor=DB.cursor()try:SQL="select * from account where account_id=%s and account_passwd=%s" %(self.account_id,self.account_passwd)cursor.execute(SQL)if cursor.fetchall():return Trueelse:return Falseexcept Exception as e:print("错误",e)finally:cursor.close()# 查询余额def query_money(self):cursor=DB.cursor()try:SQL="select money from account where account_id=%s and account_passwd=%s" %(self.account_id,self.account_passwd)cursor.execute(SQL)money=cursor.fetchone()[0]if money:return str(money.quantize(decimal.Decimal('0.00')))else:return 0.00except Exception as e:print("错误原因",e)finally:cursor.close()# 取钱（注意传入money参数）def reduce_money(self,money):cursor = DB.cursor()try:# 先调用query_money方法，查询余额has_money=self.query_money()# 所取金额小于余额则执行（注意类型转换）if decimal.Decimal(money) <= decimal.Decimal(has_money):# 进行数据更新操作SQL="update account set money=money-%s where account_id=%s and account_passwd=%s" %(money,self.account_id,self.account_passwd)cursor.execute(SQL)# rowcount进行行计数，行数为1则将数据提交给数据库if cursor.rowcount==1:DB.commit()return Trueelse:# rollback数据库回滚，行数不为1则不执行DB.rollback()return Falseelse:print("余额不足")except Exception as e:print("错误原因",e)finally:cursor.close()# 存钱# def add_moneydef main():global DBDB=pymysql.connect(host="localhost",user="root",passwd="1234",charset="utf8",database="bank")cursor=DB.cursor()from_account_id=input("请输入账号：")from_account_passwd=input("请输入密码：")account=Account(from_account_id,from_account_passwd)if account.check_account():choose=input("请输入操作：\n1、查询余额\n2、取钱\n3、存钱\n4、取卡\n")while choose!="4":# 查询if choose=="1":print("您的余额是%s元" % account.query_money())# 取钱elif choose=="2":# 先查询余额，再输入取款金额，防止取款金额大于余额money=input("您的余额是%s元,请输入取款金额" % account.query_money())# 调用reduce_money方法，money不为空则取款成功if account.reduce_money(money):print("取款成功，您的余额还有%s元" % account.query_money())else:print("取款失败！")# 存钱elif choose=="3":print("333")choose = input("请输入操作：\n1、查询余额\n2、取钱\n3、存钱\n4、取卡\n")else:print("谢谢使用！")else:print("账号或密码错误")DB.close()
main()

5、加入存钱功能

存钱功能和取钱功能相似，而且不需要考虑余额的问题，至此已完善当前所有功能

import pymysql
import decimal
DB=None
class Account():def __init__(self,account_id,account_passwd):self.account_id=account_idself.account_passwd=account_passwd# 登录检查def check_account(self):cursor=DB.cursor()try:SQL="select * from account where account_id=%s and account_passwd=%s" %(self.account_id,self.account_passwd)cursor.execute(SQL)if cursor.fetchall():return Trueelse:return Falseexcept Exception as e:print("错误",e)finally:cursor.close()# 查询余额def query_money(self):cursor=DB.cursor()try:SQL="select money from account where account_id=%s and account_passwd=%s" %(self.account_id,self.account_passwd)cursor.execute(SQL)money=cursor.fetchone()[0]if money:return str(money.quantize(decimal.Decimal('0.00')))else:return 0.00except Exception as e:print("错误原因",e)finally:cursor.close()# 取钱def reduce_money(self,money):cursor = DB.cursor()try:has_money=self.query_money()if decimal.Decimal(money) <= decimal.Decimal(has_money):SQL="update account set money=money-%s where account_id=%s and account_passwd=%s" %(money,self.account_id,self.account_passwd)cursor.execute(SQL)if cursor.rowcount==1:DB.commit()return Trueelse:DB.rollback()return Falseelse:print("余额不足")except Exception as e:print("错误原因",e)finally:cursor.close()# 存钱def add_money(self,money):cursor = DB.cursor()try:SQL="update account set money=money+%s where account_id=%s and account_passwd=%s" %(money,self.account_id,self.account_passwd)cursor.execute(SQL)if cursor.rowcount==1:DB.commit()return Trueelse:DB.rollback()return Falseexcept Exception as e:DB.rollback()print("错误原因",e)finally:cursor.close()def main():global DBDB=pymysql.connect(host="localhost",user="root",passwd="1234",charset="utf8",database="bank")cursor=DB.cursor()from_account_id=input("请输入账号：")from_account_passwd=input("请输入密码：")account=Account(from_account_id,from_account_passwd)if account.check_account():choose=input("请输入操作：\n1、查询余额\n2、取钱\n3、存钱\n4、取卡\n")while choose!="4":# 查询if choose=="1":print("您的余额是%s元" % account.query_money())# 取钱elif choose=="2":money=input("您的余额是%s元,请输入取款金额" % account.query_money())if account.reduce_money(money):print("取款成功，您的余额还有%s元" % account.query_money())else:print("取款失败！")# 存钱elif choose=="3":money=input("请输入存款金额：")if account.add_money(money):print("存款成功，您的余额还有%s元，按任意键继续\n" % (account.query_money()))else:print("存款失败，按任意键继续")choose = input("请输入操作：\n1、查询余额\n2、取钱\n3、存钱\n4、取卡\n")else:print("谢谢使用！")else:print("账号或密码错误")DB.close()
main()