相关疑难解决方法(0)

我将使用一个具体的,但假设的例子.

每个订单通常只有一个订单项:

命令:

OrderGUID   OrderNumber
=========   ============
{FFB2...}   STL-7442-1      
{3EC6...}   MPT-9931-8A

了LineItem:

LineItemGUID   Order ID Quantity   Description
============   ======== ========   =================================
{098FBE3...}   1        7          prefabulated amulite
{1609B09...}   2        32         spurving bearing

但偶尔会有一个包含两个订单项的订单:

LineItemID   Order ID    Quantity   Description
==========   ========    ========   =================================
{A58A1...}   6,784,329   5          pentametric fan
{0E9BC...}   6,784,329   5          differential girdlespring 

通常在向用户显示订单时:

SELECT Orders.OrderNumber, LineItems.Quantity, LineItems.Description
FROM Orders
    INNER JOIN LineItems 
    ON Orders.OrderID = LineItems.OrderID

我想在订单上显示单个项目.但是,由于此偶尔包含两个(或更多)商品的订单,订单将显示为重复:

OrderNumber   Quantity   Description
===========   ========   ==================== …

我正在尝试使用sqlalchemy ORM编写以下sql查询:

SELECT * FROM
   (SELECT *, row_number() OVER(w)
    FROM (select distinct on (grandma_id, author_id) * from contents) as c
    WINDOW w AS (PARTITION BY grandma_id ORDER BY RANDOM())) AS v1
WHERE row_number <= 4;

这是我到目前为止所做的:

s = Session()

unique_users_contents = (s.query(Content).distinct(Content.grandma_id,
                                                  Content.author_id)
                         .subquery())

windowed_contents = (s.query(Content,
                             func.row_number()
                             .over(partition_by=Content.grandma_id,
                                   order_by=func.random()))
                     .select_from(unique_users_contents)).subquery()

contents = (s.query(Content).select_from(windowed_contents)
            .filter(row_number >= 4)) ##  how can I reference the row_number() value?

result = contents
for content in result:
    print "%s\t%s\t%s" % (content.id, content.grandma_id,
                          content.author_id)

正如您所看到的那样,它几乎是建模的,但我不知道如何row_number() …