python知识-python操作MySQL数据库

python DB API

python访问数据库的统一接口规范





DB API-连接数据库对象connection

创建方法：MySQLdb.Connect(参数)





connection对象支持的方法





[b]DB API-数据库游标对象cursor[/b]

游标对象：用于执行查询和获取结果

cursor支持的方法：



execute方法：执行SQL，近结果从数据库返回到客户端

案例：

创建一个user表

create table user(

userid int(11) not null auto_increment,

username varchar(100) default null,

primary key (userid)

)engine=innodb auto_increment=9 default charset=utf8;

插入数据：

insert into user values ('','name1'),('','name2'),('','name3'),('','name4'),('','name5'),('','name6'),('','name7'),('','name8'),('','name9');

代码：

import MySQLdb

conn = MySQLdb.connect(host = '127.0.0.1',port = 3306,user = 'root',passwd = '',db = 'imooc',charset='utf8')

cursor = conn.cursor()

sql="select * from user"

cursor.execute(sql)

rs=cursor.fetchall()

for row in rs:

    print "userid=%s,username=%s" % row

cursor.close()

conn.close()

结果是：

userid=9,username=name1

userid=10,username=name2

userid=11,username=name3

userid=12,username=name4

userid=13,username=name5

userid=14,username=name6

userid=15,username=name7

userid=16,username=name8

userid=17,username=name9

实例演示：insert/update/delete更新数据库



import MySQLdb

conn = MySQLdb.connect(host = '127.0.0.1',port = 3306,user = 'root',passwd = '',db = 'imooc',charset='utf8')

cursor = conn.cursor()

sql_insert="insert into user (userid,username) values ('','name10')"

sql_update="update user set username='name91' where userid=9"

sql_delete="delete from user where userid=13"

try:

    cursor.execute(sql_insert)

    print cursor.rowcount

    cursor.execute(sql_update)

    print cursor.rowcount

    cursor.execute(sql_delete)

    print cursor.rowcount

    

    conn.commit()

except Exception as e:

    print e

    conn.rollback()

cursor.close()

conn.close()

实例：银行转账系统

创建表：

create table account(

acctid int(11) default null,

money int(11) default null

)engine=innodb default charset=utf8;

说明：数据库的引擎这边不能设置为MyISAM，因为它支持事物

插入数据：

insert into account values (11,110),(12,10);

代码：

# -*- coding: utf-8 -*-

"""

Created on Wed Jan 06 10:09:09 2016

@author: lenovo

"""

import sys

import MySQLdb

class TransferMoney(object):

    def __init__(self,conn):

        self.conn=conn

        

    def check_acct_avaiable(self,acctid):

        cursor=self.conn.cursor()

        try:

            sql="select * from account where acctid=%s" % acctid

            cursor.execute(sql)

            print "check_acct_avaiable:"+sql

            rs=cursor.fetchall()

            if len(rs)!=1:

                raise Exception("账号%s不存在" % acctid)

        finally:

            cursor.close()

    

    def has_enough_money(self,acctid,money):

        cursor=self.conn.cursor()

        try:

            sql="select * from account where acctid=%s and money>%s" % (acctid,money)

            cursor.execute(sql)

            print "has_enough_money:"+sql

            rs=cursor.fetchall()

            if len(rs)!=1:

                raise Exception("账号%s没有足够的钱" % acctid)

        finally:

            cursor.close()

    

    def reduce_money(self,acctid,money):

        cursor=self.conn.cursor()

        try:

            sql="update account set money=money-%s where acctid=%s" % (money,acctid)

            cursor.execute(sql)

            print "reduce_money:"+sql

            if cursor.rowcount != 1:

                raise Exception("账号%s减款失败" % acctid)

        finally:

            cursor.close()

    

    def add_money(self,acctid,money):

        cursor=self.conn.cursor()

        try:

            sql="update account set money=money+%s where acctid=%s" % (money,acctid)

            cursor.execute(sql)

            print "add_money:"+sql

            if cursor.rowcount != 1:

                raise Exception("账号%s加款失败" % acctid)

        finally:

            cursor.close()

        

    def transfer(self,source_acctid,target_acctid,money):

        try:

            self.check_acct_avaiable(source_acctid)

            self.check_acct_avaiable(target_acctid)

            self.has_enough_money(source_acctid,money)

            self.reduce_money(source_acctid,money)

            self.add_money(target_acctid,money)

            self.conn.commit()

        except Exception as e:

            self.conn.rollback()

            raise e

if __name__=="__main__":

    source_acctid=sys.argv[1]

    target_acctid=sys.argv[2]

    money=sys.argv[3]

    

    conn = MySQLdb.connect(host = '127.0.0.1',port = 3306,user = 'root',passwd = '',db = 'imooc',charset='utf8')   

    tr_money=TransferMoney(conn)

    

    try:

        tr_money.transfer(source_acctid,target_acctid,money)

    except Exception as e:

        print "出现问题："+str(e)

    finally:

        conn.close()