python操纵mysql

╰半夏微凉° 2022-05-28 09:35 155阅读 0赞

本篇对于Python操作MySQL主要使用两种方式：

*  原生模块 pymsql
 *  ORM框架 SQLAchemy

## pymsql ##

pymsql是Python中操作MySQL的模块，其使用方法和MySQLdb几乎相同。

下载安装

pip3 install pymysql

使用操作

1、执行SQL

#!/usr/bin/env python
    # -*- coding:utf-8 -*-
    import pymysql
    
    # 创建连接
    conn = pymysql.connect(host='127.0.0.1', port=3306, user='root', passwd='123', db='t1')
    # 创建游标
    cursor = conn.cursor()
    
    # 执行SQL，并返回收影响行数
    effect_row = cursor.execute("update hosts set host = '1.1.1.2'")
    
    # 执行SQL，并返回受影响行数
    #effect_row = cursor.execute("update hosts set host = '1.1.1.2' where nid > %s", (1,))
    
    # 执行SQL，并返回受影响行数
    #effect_row = cursor.executemany("insert into hosts(host,color_id)values(%s,%s)", [("1.1.1.11",1),("1.1.1.11",2)])
    
    
    # 提交，不然无法保存新建或者修改的数据
    conn.commit()
    
    # 关闭游标
    cursor.close()
    # 关闭连接
    conn.close()

2、获取新创建数据自增ID

#!/usr/bin/env python
    # -*- coding:utf-8 -*-
    import pymysql
    
    conn = pymysql.connect(host='127.0.0.1', port=3306, user='root', passwd='123', db='t1')
    cursor = conn.cursor()
    cursor.executemany("insert into hosts(host,color_id)values(%s,%s)", [("1.1.1.11",1),("1.1.1.11",2)])
    conn.commit()
    cursor.close()
    conn.close()
    
    # 获取最新自增ID
    new_id = cursor.lastrowid

3、获取查询数据

#!/usr/bin/env python
    # -*- coding:utf-8 -*-
    import pymysql
    
    conn = pymysql.connect(host='127.0.0.1', port=3306, user='root', passwd='123', db='t1')
    cursor = conn.cursor()
    cursor.execute("select * from hosts")
    
    # 获取第一行数据
    row_1 = cursor.fetchone()
    
    # 获取前n行数据
    # row_2 = cursor.fetchmany(3)
    # 获取所有数据
    # row_3 = cursor.fetchall()
    
    conn.commit()
    cursor.close()
    conn.close()
    
    注：在fetch数据时按照顺序进行，可以使用cursor.scroll(num,mode)来移动游标位置，如：
    
        cursor.scroll(1,mode='relative')  # 相对当前位置移动
        cursor.scroll(2,mode='absolute') # 相对绝对位置移动

4、fetch数据类型  
关于默认获取的数据是元祖类型，如果想要或者字典类型的数据，即：

#!/usr/bin/env python
    # -*- coding:utf-8 -*-
    import pymysql
    
    conn = pymysql.connect(host='127.0.0.1', port=3306, user='root', passwd='123', db='t1')
    
    # 游标设置为字典类型
    cursor = conn.cursor(cursor=pymysql.cursors.DictCursor)
    r = cursor.execute("call p1()")
    
    result = cursor.fetchone()
    
    conn.commit()
    cursor.close()
    conn.close()

## SQLAchemy ##

SQLAlchemy是Python编程语言下的一款ORM框架，该框架建立在数据库API之上，使用关系对象映射进行数据库操作，简言之便是：将对象转换成SQL，然后使用数据API执行SQL并获取执行结果。

安装：

pip3 install SQLAlchemy

SQLAlchemy本身无法操作数据库，其必须以来pymsql等第三方插件，Dialect用于和数据API进行交流，根据配置文件的不同调用不同的数据库API，从而实现对数据库的操作，如：

MySQL-Python
        mysql+mysqldb://<user>:<password>@<host>[:<port>]/<dbname>
    
    pymysql
        mysql+pymysql://<username>:<password>@<host>/<dbname>[?<options>]
    
    MySQL-Connector
        mysql+mysqlconnector://<user>:<password>@<host>[:<port>]/<dbname>
    
    cx_Oracle
        oracle+cx_oracle://user:pass@host:port/dbname[?key=value&key=value...]
    
    更多详见：http://docs.sqlalchemy.org/en/latest/dialects/index.html

一、内部处理  
使用 Engine/ConnectionPooling/Dialect 进行数据库操作，Engine使用ConnectionPooling连接数据库，然后再通过Dialect执行SQL语句。

#!/usr/bin/env python
    # -*- coding:utf-8 -*-
    from sqlalchemy import create_engine
    
    
    engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/t1", max_overflow=5)
    
    # 执行SQL
    # cur = engine.execute(
    # "INSERT INTO hosts (host, color_id) VALUES ('1.1.1.22', 3)"
    # )
    
    # 新插入行自增ID
    # cur.lastrowid
    
    # 执行SQL
    # cur = engine.execute(
    # "INSERT INTO hosts (host, color_id) VALUES(%s, %s)",[('1.1.1.22', 3),('1.1.1.221', 3),]
    # )
    
    
    # 执行SQL
    # cur = engine.execute(
    # "INSERT INTO hosts (host, color_id) VALUES (%(host)s, %(color_id)s)",
    # host='1.1.1.99', color_id=3
    # )
    
    # 执行SQL
    # cur = engine.execute('select * from hosts')
    # 获取第一行数据
    # cur.fetchone()
    # 获取第n行数据
    # cur.fetchmany(3)
    # 获取所有数据
    # cur.fetchall()

二、ORM功能使用

使用 ORM/Schema Type/SQL Expression Language/Engine/ConnectionPooling/Dialect所有组件对数据进行操作。根据类创建对象，对象转换成SQL，执行SQL。  
1、创建表

#!/usr/bin/env python
    # -*- coding:utf-8 -*-
    from sqlalchemy.ext.declarative import declarative_base
    from sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Index
    from sqlalchemy.orm import sessionmaker, relationship
    from sqlalchemy import create_engine
    
    engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/t1", max_overflow=5)
    
    Base = declarative_base()
    
    # 创建单表
    class Users(Base):
        __tablename__ = 'users'
        id = Column(Integer, primary_key=True)
        name = Column(String(32))
        extra = Column(String(16))
    
        __table_args__ = (
        UniqueConstraint('id', 'name', name='uix_id_name'),
            Index('ix_id_name', 'name', 'extra'),
        )
    
    
    # 一对多
    class Favor(Base):
        __tablename__ = 'favor'
        nid = Column(Integer, primary_key=True)
        caption = Column(String(50), default='red', unique=True)
    
    
    class Person(Base):
        __tablename__ = 'person'
        nid = Column(Integer, primary_key=True)
        name = Column(String(32), index=True, nullable=True)
        favor_id = Column(Integer, ForeignKey("favor.nid"))
    
    
    # 多对多
    class Group(Base):
        __tablename__ = 'group'
        id = Column(Integer, primary_key=True)
        name = Column(String(64), unique=True, nullable=False)
        port = Column(Integer, default=22)
    
    
    class Server(Base):
        __tablename__ = 'server'
    
        id = Column(Integer, primary_key=True, autoincrement=True)
        hostname = Column(String(64), unique=True, nullable=False)
    
    
    class ServerToGroup(Base):
        __tablename__ = 'servertogroup'
        nid = Column(Integer, primary_key=True, autoincrement=True)
        server_id = Column(Integer, ForeignKey('server.id'))
        group_id = Column(Integer, ForeignKey('group.id'))
    
    
    def init_db():
        Base.metadata.create_all(engine)
    
    
    def drop_db():
        Base.metadata.drop_all(engine)
    注：设置外检的另一种方式 ForeignKeyConstraint(['other_id'], ['othertable.other_id'])

2、操作表

#####################创建不同关系表
    #!/usr/bin/env python
    # -*- coding:utf-8 -*-
    from sqlalchemy.ext.declarative import declarative_base
    from sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Index
    from sqlalchemy.orm import sessionmaker, relationship
    from sqlalchemy import create_engine
    
    engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/t1", max_overflow=5)
    
    Base = declarative_base()
    
    # 创建单表
    class Users(Base):
        __tablename__ = 'users'
        id = Column(Integer, primary_key=True)
        name = Column(String(32))
        extra = Column(String(16))
    
        __table_args__ = (
        UniqueConstraint('id', 'name', name='uix_id_name'),
            Index('ix_id_name', 'name', 'extra'),
        )
    
        def __repr__(self):
            return "%s-%s" %(self.id, self.name)
    
    # 一对多
    class Favor(Base):
        __tablename__ = 'favor'
        nid = Column(Integer, primary_key=True)
        caption = Column(String(50), default='red', unique=True)
    
        def __repr__(self):
            return "%s-%s" %(self.nid, self.caption)
    
    class Person(Base):
        __tablename__ = 'person'
        nid = Column(Integer, primary_key=True)
        name = Column(String(32), index=True, nullable=True)
        favor_id = Column(Integer, ForeignKey("favor.nid"))
        # 与生成表结构无关，仅用于查询方便
        favor = relationship("Favor", backref='pers')
    
    # 多对多
    class ServerToGroup(Base):
        __tablename__ = 'servertogroup'
        nid = Column(Integer, primary_key=True, autoincrement=True)
        server_id = Column(Integer, ForeignKey('server.id'))
        group_id = Column(Integer, ForeignKey('group.id'))
        group = relationship("Group", backref='s2g')
        server = relationship("Server", backref='s2g')
    
    class Group(Base):
        __tablename__ = 'group'
        id = Column(Integer, primary_key=True)
        name = Column(String(64), unique=True, nullable=False)
        port = Column(Integer, default=22)
        # group = relationship('Group',secondary=ServerToGroup,backref='host_list')
    
    
    class Server(Base):
        __tablename__ = 'server'
    
        id = Column(Integer, primary_key=True, autoincrement=True)
        hostname = Column(String(64), unique=True, nullable=False)
    
    
    
    
    def init_db():
        Base.metadata.create_all(engine)
    
    
    def drop_db():
        Base.metadata.drop_all(engine)
    
    
    Session = sessionmaker(bind=engine)
    session = Session()

增

obj = Users(name="alex0", extra='sb')
    session.add(obj)
    session.add_all([
        Users(name="alex1", extra='sb'),
        Users(name="alex2", extra='sb'),
    ])
    session.commit()

删

session.query(Users).filter(Users.id > 2).delete()
    session.commit()

改

session.query(Users).filter(Users.id > 2).update({
       "name" : "099"})
    session.query(Users).filter(Users.id > 2).update({Users.name: Users.name + "099"}, synchronize_session=False)
    session.query(Users).filter(Users.id > 2).update({
       "num": Users.num + 1}, synchronize_session="evaluate")
    session.commit()

查

ret = session.query(Users).all()
    ret = session.query(Users.name, Users.extra).all()
    ret = session.query(Users).filter_by(name='alex').all()
    ret = session.query(Users).filter_by(name='alex').first()
    
    ret = session.query(Users).filter(text("id<:value and name=:name")).params(value=224, name='fred').order_by(User.id).all()
    
    ret = session.query(Users).from_statement(text("SELECT * FROM users where name=:name")).params(name='ed').all()

其他

#　条件
    ret = session.query(Users).filter_by(name='alex').all()
    ret = session.query(Users).filter(Users.id > 1, Users.name == 'eric').all()
    ret = session.query(Users).filter(Users.id.between(1, 3), Users.name == 'eric').all()
    ret = session.query(Users).filter(Users.id.in_([1,3,4])).all()
    ret = session.query(Users).filter(~Users.id.in_([1,3,4])).all()
    ret = session.query(Users).filter(Users.id.in_(session.query(Users.id).filter_by(name='eric'))).all()
    from sqlalchemy import and_, or_
    ret = session.query(Users).filter(and_(Users.id > 3, Users.name == 'eric')).all()
    ret = session.query(Users).filter(or_(Users.id < 2, Users.name == 'eric')).all()
    ret = session.query(Users).filter(
        or_(
            Users.id < 2,
            and_(Users.name == 'eric', Users.id > 3),
            Users.extra != ""
        )).all()
    
    
    # 通配符
    ret = session.query(Users).filter(Users.name.like('e%')).all()
    ret = session.query(Users).filter(~Users.name.like('e%')).all()
    
    # 限制
    ret = session.query(Users)[1:2]
    
    # 排序
    ret = session.query(Users).order_by(Users.name.desc()).all()
    ret = session.query(Users).order_by(Users.name.desc(), Users.id.asc()).all()
    
    # 分组
    from sqlalchemy.sql import func
    
    ret = session.query(Users).group_by(Users.extra).all()
    ret = session.query(
        func.max(Users.id),
        func.sum(Users.id),
        func.min(Users.id)).group_by(Users.name).all()
    
    ret = session.query(
        func.max(Users.id),
        func.sum(Users.id),
        func.min(Users.id)).group_by(Users.name).having(func.min(Users.id) >2).all()
    
    # 连表
    
    ret = session.query(Users, Favor).filter(Users.id == Favor.nid).all()
    
    ret = session.query(Person).join(Favor).all()
    
    ret = session.query(Person).join(Favor, isouter=True).all()
    
    
    # 组合
    q1 = session.query(Users.name).filter(Users.id > 2)
    q2 = session.query(Favor.caption).filter(Favor.nid < 2)
    ret = q1.union(q2).all()
    
    q1 = session.query(Users.name).filter(Users.id > 2)
    q2 = session.query(Favor.caption).filter(Favor.nid < 2)
    ret = q1.union_all(q2).all()