openstack-db-数据库之SQLAlchemy实战详解

最新推荐文章于 2025-03-09 19:58:41 发布

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本文详细介绍了SQL查询在数据库操作中的应用，包括基本查询、条件查询、关联查询、聚合查询、子查询等，并通过ORM（对象关系映射）技术实现数据库交互，展示如何在Python环境下使用SQLAlchemy进行高效的数据操作。

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#简单查询
print(session.query(User).all())
print(session.query(User.name, User.fullname).all())
print(session.query(User, User.name).all())
#带条件查询
print(session.query(User).filter_by(name='user1').all())
print(session.query(User).filter(User.name == "user").all())
print(session.query(User).filter(User.name.like("user%")).all())
#多条件查询
print(session.query(User).filter(and_(User.name.like("user%"), User.fullname.like("first%"))).all())
print(session.query(User).filter(or_(User.name.like("user%"), User.password != None)).all())
#sql过滤
print(session.query(User).filter("id>:id").params(id=1).all())
#关联查询
print(session.query(User, Address).filter(User.id == Address.user_id).all())
print(session.query(User).join(User.addresses).all())
print(session.query(User).outerjoin(User.addresses).all())
#聚合查询
print(session.query(User.name, func.count('*').label("user_count")).group_by(User.name).all())
print(session.query(User.name, func.sum(User.id).label("user_id_sum")).group_by(User.name).all())
#子查询
stmt = session.query(Address.user_id, func.count('*').label("address_count")).group_by(Address.user_id).subquery()
print(session.query(User, stmt.c.address_count).outerjoin((stmt, User.id == stmt.c.user_id)).order_by(User.id).all())
#exists
print(session.query(User).filter(exists().where(Address.user_id == User.id)))
print(session.query(User).filter(User.addresses.any()))

以下为映射类：

class User(Base):
__tablename__ = "users"
id = Column("id", Integer, primary_key=True)
name = Column("name", String)
fullname = Column("fullname", String)
password = Column("password", String)
addresses = relation("Address", order_by="Address.id", backref="user")
def __init__(self, id=None, name=None, fullname=None, password=None, addresses=[]):
self.id = id
self.name = name
self.fullname = fullname
self.password = password
self.addresses = addresses
def __repr__(self):
return "<User '{name}' '{fullname}' '{password}' {addresses}>".format(name=self.name, fullname=self.fullname, password=self.password, addresses=self.addresses)
class Address(Base):
__tablename__ = "address"
id = Column(Integer, primary_key=True)
email_address = Column(String, nullable=False)
user_id = Column(Integer, ForeignKey("users.id"))
#user = relation("User", backref="addresses", order_by="Address.id")
def __init__(self, email_address=None):
self.email_address = email_address
def __repr__(self):
return "<Address ({email_address}) user={user}>".format(email_address=self.email_address, user=self.user.name)