如何在 sqlAlchemy 模型的连接查询中使用 sum 和 count

Question

我有工作 SQL，需要在使用 SQLAlchemy 作为 ORM 的工作 Flask 应用程序中表示。我可以表示连接等，但在连接总和、计数和其他特定选择元素 时却一事无成u.firstname || ' ' || u.lastname。

SQL

select
  u.firstname || ' ' || u.lastname SELLER,
  count(i.id) UNIQUE_ITEMS,
  sum(i.qty) ITEMS_TOTAL,
  sum(i.qty * p.price) ORDER_AMOUNT
from
  orders o
  INNER JOIN order_items i
    on o.id = i.order_id
    and o.campaign_id = 133
  INNER JOIN products p
      ON i.product_id = p.id
  INNER JOIN users u
      ON o.user_id = u.id
GROUP BY u.id
ORDER BY sum(i.qty) DESC, sum(i.qty * p.price) DESC;

和工作 Flask 实现：

orders = Order.query.filter_by(campaign_id=campaign_id).
  join(OrderItem).
  join(Product).
  join(User).
  order_by(OrderItem.qty.desc())

如果我添加group_by(User.id)它也会抱怨我没有放入 中的所有其他元素Order。

如果功能是问题，我正在运行 Postgres 9.5

Answer 1

您正在尝试查询Order，但这不是您在原始 SQL 中查询的内容。你需要类似的东西：

query = session.query(
    (User.first_name + ' ' + User.last_name).label('seller'),
    sa.func.count(OrderItem.id).label('unique_items'),
    sa.func.sum(OrderItem.qty).label('items_total'),
    sa.func.sum(OrderItem.qty * Product.price).label('order_amount'),
).join(OrderItem).join(Product).group_by(User.id).order_by('items_total',
                                                           'order_amount')

将所有内容放在一个示例中，向您展示发生了什么：

import sqlalchemy as sa
from sqlalchemy.ext.declarative import declarative_base
from decimal import Decimal

engine = sa.create_engine('sqlite:///:memory:')
Base = declarative_base()
session = sa.orm.sessionmaker(bind=engine)()

class OrderItem(Base):
    __tablename__ = 'order'

    id = sa.Column('id', sa.Integer, primary_key=True)
    product_id = sa.Column('product_id', sa.Integer, sa.ForeignKey('product.id'))
    user_id = sa.Column('user_id', sa.Integer, sa.ForeignKey('user.id'))
    qty = sa.Column('qty', sa.Integer)

class Product(Base):
    __tablename__ = 'product'

    id = sa.Column('id', sa.Integer, primary_key=True)
    price = sa.Column('price', sa.Numeric(14,2))

class User(Base):
    __tablename__ = 'user'

    id = sa.Column('id', sa.Integer, primary_key=True)
    first_name = sa.Column('first_name', sa.Text)
    last_name = sa.Column('last_name', sa.Text)

Base.metadata.create_all(engine)

engine.echo = True

session.add(User(id=42, first_name='John', last_name='Cleese'))
session.add(User(id=13, first_name='Sir', last_name='Robin'))
session.add(Product(id=1, price=Decimal('2.10')))
session.add(OrderItem(product_id=1, user_id=42, qty=9))
session.add(OrderItem(product_id=1, user_id=42, qty=2))
session.add(OrderItem(product_id=1, user_id=13, qty=2))
session.add(OrderItem(product_id=1, user_id=13, qty=3))
session.add(OrderItem(product_id=1, user_id=13, qty=20))
session.commit()

query = session.query(
    (User.first_name + ' ' + User.last_name).label('seller'),
    sa.func.count(OrderItem.id).label('unique_items'),
    sa.func.sum(OrderItem.qty).label('items_total'),
    sa.func.sum(OrderItem.qty * Product.price).label('order_amount'),
).join(OrderItem).join(Product).group_by(User.id).order_by('items_total',
                                                           'order_amount')


print('{0:=^40}\n{1:^40}\n{0:=^40}'.format('=', 'Query'))
results = [row for row in session.execute(query)]
print('{0:=^40}\n{1:^40}\n{0:=^40}'.format('=', 'Results'))
for row in results:
    print(dict(row))