Python使用sqlalchemy模块连接数据库操作示例

本文实例讲述了python/' target='_blank'>python使用sqlalchemy模块连接数据库操作。分享给大家供大家参考，具体如下：

安装：

pip install sqlalchemy# 安装数据库驱动：pip install pymysql/' target='_blank'>mysqlpip install cx_oracle

举例：（在url后面加入?charset=utf8可以防止乱码）

from sqlalchemy import create_engineengine=create_engine('MySQL+pymysql://username:password@hostname:port/dbname', echo=True) #echo=True 打印sql语句信息

create_engine接受一个url，格式为：

# '数据库类型+数据库驱动名称://用户名:口令@机器地址:端口号/数据库名'# 常用的engine = create_engine('sqlite:///:memory:', echo=True)   # sqlite内存engine = create_engine('sqlite:///./cnblogblog.db',echo=True) # sqlite文件engine = create_engine("mysql+pymysql://username:password@hostname:port/dbname",echo=True) # mysql+pymysqlengine = create_engine('mssql+pymssql://username:password@hostname:port/dbname',echo=True) # mssql+pymssqlengine = create_engine('postgresql://scott:tiger@hostname:5432/dbname') # postgresql示例engine = create_engine('oracle://scott:tiger@hostname:1521/sidname') # oracleengine = create_engine('oracle+cx_oracle://scott:tiger@tnsname') #pdb就可以用tns连接

简单demo：

from sqlalchemy import create_engine, Column, Integer, Stringfrom sqlalchemy.orm import sessionmakerfrom sqlalchemy.ext.declarative import declarative_base engine = create_engine('oracle://spark:a@orclpdb',echo=True) #echo要求打印sql语句等调试信息session_maker = sessionmaker(bind=engine)session = session_maker()Base = declarative_base()#对应一张表class Student(Base):   __tablename__ = 'STUDENT'  id = Column('STUID', Integer, primary_key=True)  name = Column('STUNAME', String(32), nullable=False)  age = Column('STUAGE', Integer)  def __repr__(self):    return '<Student(id:%s, name:%s, age:%s)>' % (self.id, self.name, self.age)Base.metadata.create_all(engine) #若存在STUDENT表则不做，不存在则创建。queryObject = session.query(Student).order_by(Student.id.desc())for ins in queryObject:  print(ins.id, ins.name, ins.age)'''4 hey 243 lwtxxs 272 gyb 891 ns 23'''

将查询结果映射为DataFrame：

import pandas as pddf = pd.read_sql(session.query(Student).filter(Student.id > 1).statement, engine) print(df)'''  STUID STUNAME STUAGE0   4   hey   241   2   gyb   892   3 lwtxxs   27'''

查询：

session的query方法除了可以接受Base子类对象作为参数外，还可以是字段，如：

query = session.query(Student.name, Student.age) # query为一个sqlalchemy.orm.query.Query对象for stu_name, stu_age in query:  print(stu_name, stu_age)

查询条件filter：

# = / likequery.filter(Student.name == 'wendy')query.filter(Student.name.like('%ed%'))# inquery.filter(Student.name.in_(['wendy', 'jack']))query.filter(Student.name.in_(    session.query(User.name).filter(User.name.like('%ed%'))))# not inquery.filter(~Student.name.in_(['ed', 'wendy', 'jack']))# is null / is not nullquery.filter(Student.name == None)query.filter(Student.name.is_(None))query.filter(Student.name != None)query.filter(Student.name.isnot(None))# andfrom sqlalchemy import and_, or_query.filter(and_(Student.name == 'ed', Student.age != 23))query.filter(Student.name == 'ed', Student.age != 23)query.filter(Student.name == 'ed').filter(Student.age != 23)# orquery.filter(or_(Student.name == 'ed', Student.name == 'wendy'))# matchquery.filter(Student.name.match('wendy'))

Query的方法：

all()方法以列表形式返回结果集：

from sqlalchemy import or_, and_queryObject = session.query(Student).filter(or_(Student.id == 1, Student.id == 2))print(queryObject.all())  # [<Student(id:1, name:ns, age:23)>, <Student(id:2, name:gyb, age:89)>]queryObject = session.query(Student.name).filter(or_(Student.id == 1, Student.id == 2))print(queryObject.all())  # [('ns',), ('gyb',)]

first()方法返回单个结果。（若结果集为空则返回None）

print(queryObject.first()) 　#　('ns',)

one()方法返回单个结果，与first()方法不同的是：当结果集中没有元素或有多于一个元素会抛出异常。
one_or_none()方法同one()一样，不同是结果集为空则返回None，为多个抛出异常。

查询数量：

from sqlalchemy import funcsession.query(func.count(Student.id)).scalar()　# SELECT count("STUDENT"."STUID") AS count_1 FROM "STUDENT"

分组：

session.query(func.count(Student.id), Student.name).group_by(Student.name).all()

嵌套SQL语句：

from sqlalchemy import textquery = session.query(Student.id, Student.name).filter(text('stuid>2'))query = session.query('stuid', 'stuname', 'stuage').from_statement(\text("select * from student where stuname=:stuname")).params(stuname='hey').all()  #[(4, 'hey', 24)]

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希望本文所述对大家Python程序设计有所帮助。