python操作SQL

pymysql

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

一、下载安装

pip3 install pymysql

二、操作使用

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='', 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='', 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='', 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='', 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()

SQLAlchemy

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

 #!/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()

表结构加数据库连接

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

增

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

删

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

改

 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()

查

 #　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()

其他