Python操作MySQL数据库详解

2020-07-13 17:14:22LanceLee数据爬虫847

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前言

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1. MySQL Connector

1.1 创建连接

 import mysql.connector
 config={
     "host":"localhost","port":"3306",
     "user":"root","password":"password",
     "database":"demo"
 }
 con=mysql.connector.connect(**config)
 import mysql.connector
 config={
     "host":"localhost","port":"3306",
     "user":"root","password":"password",
     "database":"demo"
 }
 con=mysql.connector.connect(**config)

1.2 Cursor

 import mysql.connector
 con=mysql.connector.connect(
     host="localhost",port="3306",
     user="root",password="password",
     database="demo"
 )
 cursor=con.cursor()
 sql="SELECT empno,job,sal FROM t_bonus;"
 cursor.execute(sql)
 print(type(cursor))
 for i in cursor:
     print(i)
 con.close()
 
 Result:
     <class 'mysql.connector.cursor_cext.CMySQLCursor'>
     (7369, 'CLERK', Decimal('8000.00'))
     (7499, 'SALESMAN', Decimal('1600.00'))
     (7521, 'SALESMAN', Decimal('1250.00'))
     (7566, 'MANAGER', Decimal('2975.00'))
     (7654, 'SALESMAN', Decimal('1250.00'))
     (7698, 'MANAGER', Decimal('2850.00'))
     (7782, 'MANAGER', Decimal('2450.00'))
     (7788, 'ANALYST', Decimal('3000.00'))
     (7839, 'PRESIDENT', Decimal('5000.00'))
     (7844, 'SALESMAN', Decimal('1500.00'))
     (7900, 'CLERK', Decimal('950.00'))
     (7902, 'ANALYST', Decimal('3000.00'))
     (7934, 'CLERK', Decimal('1300.00'))

1.3 SQL注入攻击

username=1 OR 1=1 password=1 OR 1=1
在使用字符串直接拼接时OR之前不管对错，与OR结合都为true
解决方法——预编译（也可以提高速度）

username="1 OR 1=1"
 password="1 OR 1=1"
 sql="SELECT COUNT(*) FROM t_user WHERE username=%s AND AES_DECRYPT(UNHEX(password),'helloWorld')=%s"
 cursor.execute(sql,(username,password))
 print(cursor.fetchone()[0])

1.4 事务管理和异常处理

sql连接和使用异常处理异常

 import mysql.connector
 try:
     con=mysql.connector.connect(
         host="localhost",port="3306",
         user="root",password="password",
         database="demo"
     )
     con.start_transaction()
     cursor=con.cursor()
     sql="INSERT INTO t_dept(deptno,dname,loc) VALUES(%s,%s,%s);"
     cursor.execute(sql,(60,"SALES","HUBAI"))
     con.commit()
 except Exception as e:
     if "con" in dir():
         con.rollback()
     print(e)
 finally:
     if "con" in dir():
         con.close()

1.5 删除数据

import mysql.connector,mysql.connector.pooling
 config={
     "host": "localhost", "port": "3306",
     "user": "root", "password": "password",
     "database": "demo"
 }
 try:
     pool=mysql.connector.pooling.MySQLConnectionPool(**config,pool_size=5)
     con=pool.get_connection()
     con.start_transaction()
     cursor = con.cursor()
     sql = "DELETE FROM t_dept WHERE deptno=%s"
     cursor.execute(sql, (70,))
     con.commit()
 except Exception as e:
     if "con" in dir():
         con.rollback()
     print(e)
 # do not need to close con

executemany() 反复执行一条SQL语句

 import mysql.connector,mysql.connector.pooling
 config={
     "host": "localhost", "port": "3306",
     "user": "root", "password": "password",
     "database": "demo"
 }
 try:
     pool=mysql.connector.pooling.MySQLConnectionPool(**config,pool_size=5)
     con=pool.get_connection()
     con.start_transaction()
     cursor = con.cursor()
     sql = "INSERT INTO t_dept(deptno,dname,loc) VALUES(%s,%s,%s);"
     date=[[70,"SALES","BEIJING"],[80,"ACTOR","SHANGHAI"]]
     cursor.executemany(sql, date)
     con.commit()
 except Exception as e:
     if "con" in dir():
         con.rollback()
     print(e)
 # do not need to close con

2. 数据库连接池

数据库的连接是昂贵的，一个连接要经过TCP三次握手，四次挥手，而且一台计算机的最大线程数也是有限的
数据库连接池技术就是先创建好连接，再直接拿出来使用

import mysql.connector,mysql.connector.pooling
 config={
     "host": "localhost", "port": "3306",
     "user": "root", "password": "password",
     "database": "demo"
 }
 try:
     pool=mysql.connector.pooling.MySQLConnectionPool(**config,pool_size=5)
     con=pool.get_connection()
     con.start_transaction()
     cursor = con.cursor()
     sql = "INSERT INTO t_dept(deptno,dname,loc) VALUES(%s,%s,%s);"
     cursor.execute(sql, (70, "SALES", "HUBAI"))
     con.commit()
 except Exception as e:
     if "con" in dir():
         con.rollback()
     print(e)
 # do not need to close con

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