# Assume these classes are fully defined, including relationships
class User(Base):
  pass
class Order(Base):
  pass

# Requested: SELECT DISTINCT user.id FROM user, order WHERE user.id = order.user_id
session.query(User.id).select_from(User, Order).filter(User.id == Order.user_id).distinct()
# Produces: SELECT DISTINCT user.id AS user_id FROM user, order WHERE user.id = order.user_id