可以将and（）表达式与.outerjoin（）一起使用。仅举两种型号的示例：

from sqlalchemy import and_

class A(Base):
    __tablename__ = 'a'
    id = Column(Integer, primary_key=True)

class B(Base):
    __tablename__ = 'b'
    id = Column(Integer, primary_key=True)
    a_id = Column(Integer)
    flag = Column(String)

a = A()
session.add(a)
session.commit()

# just a few records. without flag + with flag

b1 = B(a_id=a.id)
b2 = B(a_id=a.id, flag='Cs_Is_Better')

session.add(b1)
session.add(b2)
session.commit()

query = session.query(A).outerjoin(B, (and_(A.id == B.a_id, B.flag == 'Cs_Is_Better')))

print(query)

# SELECT a.id AS a_id

# FROM a LEFT OUTER JOIN b ON a.id = b.a_id AND b.flag = %(flag_1)s

print(query.all())  # [<__main__.A object at 0x112fb4780>]

所以只要给 outerjoin :

.outerjoin(ModelName, (and_(...))

希望这有帮助。