SQL most recent using row_number() over partition

问题:

I'm working with some web clicks data, and am just looking for the most recent page_name with the user_id visited (by a timestamp). Using the below code, the user_id is repeated and page_name with shown, with sorted descending. However, I would just like recent_click always = 1. The query when complete will be used as a subquery in a larger query.

Here is my current code:

 SELECT user_id,
 page_name,
 row_number() over(partition by session_id order by ts desc) as recent_click
 from clicks_data;

 user_id |  page_name  |  recent_click
 --------+-------------+--------------
 0001    |  login      |  1
 0001    |  login      |  2
 0002    |  home       |  1

回答1:

You should be able to move your query to a subquery and add where criteria:

SELECT user_id, page_name, recent_click
FROM (
  SELECT user_id,
         page_name,
         row_number() over (partition by session_id order by ts desc) as recent_click
  from clicks_data
) T
WHERE recent_click = 1

回答2:

You should move the row_number() function into a subquery and then filter it in the outer query.
Something like this:

SELECT * FROM (
    SELECT
         [user_id]
        ,[page_name]
        ,ROW_NUMBER() OVER (PARTITION BY [session_id] 
                            ORDER BY [ts] DESC) AS [recent_click]
    FROM [clicks_data]
)x 
WHERE [recent_click] = 1