python3 的 mysql 简单操作

Posted 2020-10-10

一、python 提供的 db 接口

pymysql

两个基本对象： connection、cursor

连接示例

# connect_demo.py

import pymysql

db = pymysql.connect(‘localhost‘, ‘root‘, ‘root‘, ‘imooc‘, charset=‘utf8‘)
cursor = db.cursor()

print(db)
print(cursor)

cursor.close()
db.close()

输出

<pymysql.connections.Connection object at 0x7f1e2a852278>
<pymysql.cursors.Cursor object at 0x7f1e2880e668>

操作游标

# cursor_demo.py

import pymysql

db = pymysql.connect(‘localhost‘, ‘root‘, ‘root‘, ‘imooc‘, charset=‘utf8‘)
cursor = db.cursor()

sql = ‘select * from user‘

cursor.execute(sql)

print(cursor.rowcount)

result = cursor.fetchall()
print(result)

for row in result:
   print(row[0],‘:‘, row[1])

cursor.close()
db.close()

输出

((1, ‘lisi‘), (2, ‘zhangsan‘), (3, ‘liuqi‘), (4, ‘white‘))
1 : lisi
2 : zhangsan
3 : liuqi
4 : white

 

二、增删改查

# curd_demo.py

import pymysql

db = pymysql.connect(‘localhost‘, ‘root‘, ‘root‘, ‘imooc‘, charset=‘utf8‘)
cursor = db.cursor()

sql_select = "select * from user"
sql_insert = "insert into user(userid, username) values(DEFAULT, ‘wuliu‘)"
sql_update = "update user set username=‘liuqi‘ where userid=3"
sql_delete = "delete from user where userid>4"

cursor.execute(sql_select)
result = cursor.fetchall()
print(result)

try:
    cursor.execute(sql_insert)
    result = cursor.rowcount
    print(result)

    cursor.execute(sql_update)
    result = cursor.rowcount
    print(result)

    cursor.execute(sql_delete)
    result = cursor.rowcount
    print(result)

    db.commit()
except Exception as e:
    print(e)
    db.rollback()

cursor.close()
db.close()

输出

((1, ‘lisi‘), (2, ‘zhangsan‘), (3, ‘liuqi‘), (4, ‘white‘))
1
0
1

 

三、事务的小示例

# bank_demo.py

# coding:utf8

import sys
import pymysql

class TransferMoney(object):
    def __init__(self, conn):
        self.conn = conn

    def check_acct_available(self, acctid):
        cursor = self.conn.cursor()
        try:
            sql = "select * from account where acctid=%s" % acctid
            cursor.execute(sql)
            print("check_acct_available:" + sql)
            rs = cursor.fetchall()
            if len(rs) != 1:
                raise Exception("账号不存在" % 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("chas_enough_mone:" + sql)
            rs = cursor.fetchall()
            if len(rs) != 1:
                raise Exception("账号%s余额不足" % 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("rad_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_available(source_acctid)
            self.check_acct_available(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 = pymysql.connect(‘localhost‘, ‘root‘, ‘root‘, ‘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()

命令行运行

 python bank_demo.py 3 1 1000

输出

check_acct_available:select * from account where acctid=3
check_acct_available:select * from account where acctid=1
chas_enough_mone:select * from account where acctid=3 and money>1000
reduce_money:update account set money=money - 1000 where acctid=3
rad_money:update account set money=money + 1000 where acctid=1