sqlalchemy常用操作

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

from sqlalchemy import Column, String, create_engine, Integer, MetaData, Table
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

# 创建对象的基类:
Base = declarative_base()


# 定义User对象:
class User(Base):
    # 表的名字:
    __tablename__ = 'user'

    # 表的结构:
    id = Column(Integer(), primary_key=True)
    name = Column(String(20))
    age = Column(Integer())


# 初始化数据库连接:
engine = create_engine('mysql+pymysql://root:password@localhost:3306/common')
# 创建DBSession类型:
DBSession = sessionmaker(bind=engine)
# 创建表
Base.metadata.create_all(engine)


def add_user(name, age):
    # 创建session对象:
    session = DBSession()
    # 创建新User对象:
    new_user = User(name=name, age=age)
    # 添加到session:
    session.add(new_user)
    # 提交即保存到数据库:
    session.commit()
    # 关闭session:
    session.close()


def get_user(name):
    # 创建Session:
    session = DBSession()
    # 创建Query查询，filter是where条件，最后调用one()返回唯一行，如果调用all()则返回所有行:
    user = session.query(User).filter(User.name == name).one()
    # 打印类型和对象的name属性:
    print('age:', user.age)
    print('name:', user.name)
    # 关闭Session:
    session.close()



################################################操作已有数据库###########################################################################

metadata = MetaData(bind=engine)


class Province(Base):
    '''映射已有的数据库，传入三个参数：数据库名称、metadata（绑定接口）、autoload=True'''
    __table__ = Table('province', metadata, autoload=True)


def get_pname_from_exist_database(code):
    session = DBSession()
    target = session.query(Province).filter(Province.code == code).one()
    print('code:', target.code)
    print('name:', target.pname)
    # 关闭Session:
    session.close()


if __name__ == '__main__':
    add_user('user01',22)
    get_user('user01')
    
    #查询已有数据库
    get_pname_from_exist_database('ZJ')

数据去重：

CREATE TABLE table_temp AS
SELECT * FROM table GROUP BY title, SID;

DROP TABLE table;
RENAME TABLE table_temp TO table;