Python MySQL数据库基本操作及项目示例详解

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_id
        self.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False
            if cursor.fetchall():
                return True
            else:
                return False

        except 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_money
    
def 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_id
        self.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 True
            else:
                return False
        except 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money
            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]
            # 如果账户有钱就返回金额,没钱返回0.00
            if 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 0.00
        except Exception as e:
            print("错误原因",e)
        finally:
            cursor.close()

def main():
    global DB
    DB=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_id
        self.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 True
            else:
                return False
        except 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 0.00
        except 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 True
                else:
                    # rollback数据库回滚,行数不为1则不执行
                    DB.rollback()
                    return False
            else:
                print("余额不足")
        except Exception as e:
            print("错误原因",e)
        finally:
            cursor.close()
            
    # 存钱
    # def add_money

def main():
    global DB
    DB=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_id
        self.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 True
            else:
                return False
        except 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 0.00
        except 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 True
                else:
                    DB.rollback()
                    return False
            else:
                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 True
            else:
                DB.rollback()
                return False
        except Exception as e:
            DB.rollback()
            print("错误原因",e)
        finally:
            cursor.close()

def main():
    global DB
    DB=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() 

以上就是Python MySQL数据库基本操作及项目示例详解 的详细内容,更多关于Python MySQL数据库操作的资料请关注脚本之家其它相关文章!

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