本文实例讲述了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

pip install cx_oracle

举例：(在url后面加入?charset=utf8可以防止乱码)

from sqlalchemy import create_engine

engine=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+pymysql

engine = create_engine('mssql+pymssql://username:password@hostname:port/dbname',echo=True) # mssql+pymssql

engine = create_engine('postgresql://scott:tiger@hostname:5432/dbname') # postgresql示例

engine = create_engine('oracle://scott:tiger@hostname:1521/sidname') # oracle

engine = 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, String

from sqlalchemy.orm import sessionmaker

from 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 '' % (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 24

3 lwtxxs 27

2 gyb 89

1 ns 23

'''

将查询结果映射为DataFrame：

import pandas as pd

df = pd.read_sql(session.query(Student).filter(Student.id > 1).statement, engine)

print(df)

'''

STUID STUNAME STUAGE

0 4 hey 24

1 2 gyb 89

2 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：

# = / like

query.filter(Student.name == 'wendy')

query.filter(Student.name.like('%ed%'))

# in

query.filter(Student.name.in_(['wendy', 'jack']))

query.filter(Student.name.in_(

session.query(User.name).filter(User.name.like('%ed%'))

))

# not in

query.filter(~Student.name.in_(['ed', 'wendy', 'jack']))

# is null / is not null

query.filter(Student.name == None)

query.filter(Student.name.is_(None))

query.filter(Student.name != None)

query.filter(Student.name.isnot(None))

# and

from 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)

# or

query.filter(or_(Student.name == 'ed', Student.name == 'wendy'))

# match

query.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()) # [, ]

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 func

session.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 text

query = 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)]

希望本文所述对大家Python程序设计有所帮助。