Python 进阶(四):数据库操作之 MySQL

1. 简介

MySQL 是目前使用最广泛的数据库之一,它有着良好的性能,能够跨平台,支持分布式,能够承受高并发。如果还没有安装 MySQL,下载地址:https://dev.mysql.com/downloads/mysql/5.7.html,安装参考:https://jingyan.baidu.com/article/fc07f989b298ca12ffe519b6.html。

Python 大致有如下 5 种方式操作 MySQL。

  • MySQL-python

MySQL-python 也称 MySQLdb,基于 C 库开发,曾经是一个十分流行的 MySQL 驱动,具有出色的性能,但其早已停更,仅支持 Python2,不支持 Python3,现在基本不推荐使用了,取而代之的是它的衍生版。

  • mysqlclient

MySQLdb 的 Fork 版本,完全兼容 MySQLdb,支持 Python3,它是 Django ORM 的依赖工具,如果你喜欢用原生 SQL 操作数据库,那么推荐使用它。

  • PyMySQL

PyMySQL 采用纯 Python 开发,兼容 MySQLdb,性能不如 MySQLdb,安装方便,支持 Python3。

  • peewee

peewee 是一个流行的 ORM 框架,实现了对象与数据库表的映射,兼容多种数据库,我们无需知道原生 SQL,只要了解面向对象的思想就可以简单、快速的操作相应数据库,支持 Python3。

  • SQLAlchemy

SQLAlchemy 是一个 ORM 框架,同时也支持原生 SQL,支持 Python3,它类似于 Java 的 Hibernate 框架。

2. 实际操作

因为 MySQLdb 不支持 Python3,这里我们只介绍其中后 4 中方式的使用,先使用如下建表语句创建一张简单的数据库表。

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CREATE TABLE student (  id int(10) AUTO_INCREMENT PRIMARY KEY,  name varchar(255) NOT NULL,  age int(10) NOT NULL);

2.1 mysqlclient

执行 pip install mysqlclient 进行安装,看一下具体操作。

新增

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import MySQLdb
connect = MySQLdb.connect( # 主机 host='localhost', # 端口号 port=3306, # 用户名 user='root', # 密码 passwd='root', # 数据库名称 db='test', # 指定字符的编、解码格式 use_unicode=True, charset='utf8')# 先获取游标,再进行相应 SQL 操作cursor = connect .cursor()# 执行新增 SQLsql = 'insert into student (name, age) values(%s,%s);'data = [ ('张三', '22'), ('李四', '23')]cursor.executemany(sql, data)# 提交connect.commit()# 关闭cursor.close()connect.close()

查询

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import MySQLdb
connect = MySQLdb.connect( host='localhost', port=3306, user='root', passwd='root', db='test', use_unicode=True, charset='utf8')cursor = connect.cursor()cursor.execute('SELECT * FROM student')print(cursor.fetchall())cursor.close()connect.close()

cursor 查看方法

  • fetchone() 获取结果集的下一行
  • fetchmany(size) 获取结果集的下几行务
  • fetchall() 获取结果集中剩下的所有行

修改

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import MySQLdb
connect = MySQLdb.connect( host='localhost', port=3306, user='root', passwd='root', db='test', use_unicode=True, charset='utf8')cursor = connect.cursor()cursor.execute("UPDATE student SET name='张四' WHERE id = 1")connect.commit()cursor.close()connect.close()

删除

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import MySQLdb
connect = MySQLdb.connect( host='localhost', port=3306, user='root', passwd='root', db='test', use_unicode=True, charset='utf8')cursor = connect.cursor()cursor.execute("DELETE FROM student WHERE id = 1")connect.commit()cursor.close()connect.close()

2.2 PyMySQL

执行 pip install pymysql 进行安装,使用方式与 mysqlclient 基本类似。

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import pymysql
connect = pymysql.connect( host='localhost', port=3306, user='root', password='root', database='test', charset='utf8')cursor = connect.cursor()sql = 'insert into student (name, age) values(%s,%s);'data = [ ('张三', '22'), ('李四', '23')]cursor.executemany(sql, data)connect.commit()cursor.execute('SELECT * FROM student')print(cursor.fetchall())cursor.close()connect.close()

2.3 peewee

执行 pip install peewee 进行安装,看一下具体操作。

定义映射类

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from peewee import *
# 连接数据库db = MySQLDatabase('test', host='localhost', port=3306, user='root', passwd='root', charset='utf8')# 映射类class Teacher(Model): id = AutoField(primary_key=True) name = CharField() age = IntegerField() class Meta: database = db# 创建表db.create_tables([Teacher])

新增

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from peewee import *
db = MySQLDatabase('test', host='localhost', port=3306, user='root', passwd='root', charset='utf8')class Teacher(Model): id = AutoField(primary_key=True) name = CharField() age = IntegerField() class Meta: database = dbt1 = Teacher(name='张三', age=22)t2 = Teacher(name='李四', age=33)t3 = Teacher(name='王五', age=33)t1.save()t2.save()t3.save()

查询

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from peewee import *
db = MySQLDatabase('test', host='localhost', port=3306, user='root', passwd='root', charset='utf8')class Teacher(Model): id = AutoField(primary_key=True) name = CharField() age = IntegerField() class Meta: database = db# 查询单条数据t = Teacher.get(Teacher.id == 1)print('name:', t.name)# 查询多条ts = Teacher.select().where(Teacher.age == 33)for t in ts: print('name:', t.name)

修改

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from peewee import *
db = MySQLDatabase('test', host='localhost', port=3306, user='root', passwd='root', charset='utf8')class Teacher(Model): id = AutoField(primary_key=True) name = CharField() age = IntegerField() class Meta: database = dbt = Teacher.update({Teacher.name: '张四'}).where(Teacher.id == 1)t.execute()

删除

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from peewee import *
db = MySQLDatabase('test', host='localhost', port=3306, user='root', passwd='root', charset='utf8')class Teacher(Model): id = AutoField(primary_key=True) name = CharField() age = IntegerField() class Meta: database = dbTeacher.delete().where(Teacher.id == 2).execute()

2.4 SQLAlchemy

执行 pip install sqlalchemy 进行安装,看一下具体操作。

定义映射类

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from sqlalchemy import create_enginefrom sqlalchemy.ext.declarative import declarative_basefrom sqlalchemy import Column, Integer, String
engine = create_engine('mysql+mysqldb://root:root@localhost:3306/test?charset=utf8', # 打印执行语句 echo=True, # 连接池大小 pool_size=10, # 指定时间内回收连接 pool_recycle=3600)# 映射基类Base = declarative_base()# 具体映射类class Teacher(Base): # 指定映射表名 __tablename__ = 'teacher' # 映射字段 id = Column(Integer, primary_key=True) name = Column(String(30)) age = Column(Integer)# 创建表Base.metadata.create_all(engine)

新增

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from sqlalchemy import create_enginefrom sqlalchemy.ext.declarative import declarative_basefrom sqlalchemy import Column, Integer, Stringfrom sqlalchemy.orm import sessionmaker
engine = create_engine('mysql+mysqldb://root:root@localhost:3306/test?charset=utf8', # 打印执行语句 echo=True, # 连接池大小 pool_size=10, # 指定时间内回收连接 pool_recycle=3600)# 映射基类Base = declarative_base()# 具体映射类class Teacher(Base): # 指定映射表名 __tablename__ = 'teacher' # 映射字段 id = Column(Integer, primary_key=True) name = Column(String(30)) age = Column(Integer)Session = sessionmaker(bind=engine)# 创建 Session 类实例session = Session()ls = []t1 = Teacher(name='张三', age=22)t2 = Teacher(name='李四', age=33)t3 = Teacher(name='王五', age=33)ls.append(t1)ls.append(t2)ls.append(t3)session.add_all(ls)session.commit()session.close()

查询

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from sqlalchemy import create_enginefrom sqlalchemy.ext.declarative import declarative_basefrom sqlalchemy import Column, Integer, Stringfrom sqlalchemy.orm import sessionmaker
engine = create_engine('mysql+mysqldb://root:root@localhost:3306/test?charset=utf8', # 打印执行语句 echo=True, # 连接池大小 pool_size=10, # 指定时间内回收连接 pool_recycle=3600)# 映射基类Base = declarative_base()# 具体映射类class Teacher(Base): # 指定映射表名 __tablename__ = 'teacher' # 映射字段 id = Column(Integer, primary_key=True) name = Column(String(30)) age = Column(Integer)Session = sessionmaker(bind=engine)# 创建 Session 类实例session = Session()# 查询一条数据,filter 相当于 where 条件t = session.query(Teacher).filter(Teacher.id==1).one()print('---', t.name)# 查询所有数据ts = session.query(Teacher).filter(Teacher.age==33).all()for t in ts: print('===', t.name)

修改

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from sqlalchemy import create_enginefrom sqlalchemy.ext.declarative import declarative_basefrom sqlalchemy import Column, Integer, Stringfrom sqlalchemy.orm import sessionmaker
engine = create_engine('mysql+mysqldb://root:root@localhost:3306/test?charset=utf8', # 打印执行语句 echo=True, # 连接池大小 pool_size=10, # 指定时间内回收连接 pool_recycle=3600)# 映射基类Base = declarative_base()# 具体映射类class Teacher(Base): # 指定映射表名 __tablename__ = 'teacher' # 映射字段 id = Column(Integer, primary_key=True) name = Column(String(30)) age = Column(Integer)Session = sessionmaker(bind=engine)# 创建 Session 类实例session = Session()t = session.query(Teacher).filter(Teacher.id==1).one()print('修改前名字-->', t.name)t.name = '张四'session.commit()print('修改后名字-->', t.name)

删除

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from sqlalchemy import create_enginefrom sqlalchemy.ext.declarative import declarative_basefrom sqlalchemy import Column, Integer, Stringfrom sqlalchemy.orm import sessionmaker
engine = create_engine('mysql+mysqldb://root:root@localhost:3306/test?charset=utf8', # 打印执行语句 echo=True, # 连接池大小 pool_size=10, # 指定时间内回收连接 pool_recycle=3600)# 映射基类Base = declarative_base()# 具体映射类class Teacher(Base): # 指定映射表名 __tablename__ = 'teacher' # 映射字段 id = Column(Integer, primary_key=True) name = Column(String(30)) age = Column(Integer)Session = sessionmaker(bind=engine)# 创建 Session 类实例session = Session()t = session.query(Teacher).filter(Teacher.id==1).one()session.delete(t)session.commit()

 

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