Enrich website log data with user id in SQL

Assume that we have typical session log from the website with cookies and user id (in case he/she provided credentials):

cookie      id  timestamp
af312b452c  .   31-03-11 1:44 PM
af312b452c  .   31-03-11 1:46 PM
af312b452c  .   31-03-11 1:48 PM
af312b452c  .   31-03-11 1:51 PM
af312b452c  .   31-03-11 1:53 PM
af312b452c  .   31-03-11 1:56 PM
af312b452c  1   31-03-11 1:58 PM
af312b452c  1   31-03-11 2:01 PM

31-03-11 1:58 PM - user logged-in, so since then we are tracking his/her activity alongside with user_id.

I want to enrich such data by filling missing fields backwards to have complete information what particular user has seen on the webpage:

cookie      id  timestamp
af312b452c  1   31-03-11开发者_如何学编程 1:44 PM
af312b452c  1   31-03-11 1:46 PM
af312b452c  1   31-03-11 1:48 PM
af312b452c  1   31-03-11 1:51 PM
af312b452c  1   31-03-11 1:53 PM
af312b452c  1   31-03-11 1:56 PM
af312b452c  1   31-03-11 1:58 PM
af312b452c  1   31-03-11 1:58 PM

What will be the best way to do it in SQL?

Notes:

• whole table has many rows,
• users can have multiple cookies.
• a particular cookie value may have been used for a different user at some point in the past

Thank you all in advance.

I would start by creating a function that would get me the most recent logged in ID of a cookie given that cookie and the timestamp you logged that cookie (psuedocode off the top of my head, apologies if something is off):

CREATE FUNCTION getFutureLogin(in_cookie VARCHAR, in_timestamp DATETIME) RETURNS INT AS
BEGIN
  DECLARE logged_in_id IN

  SELECT logged_in_id = TOP 1 id
  FROM T_NAME
  WHERE cookie = in_cookie
  AND timestamp > in_timestamp
  AND id IS NOT NULL
  ORDER BY timestamp ASC

  RETURN logged_in_id
END

From there, it's a simple update that you'd probably schedule a job to do sometime.

UPDATE T_NAME SET id = getFutureLogin(cookie, timestamp) WHERE id IS NULL

May not be the most straightforward or fastest way, but it would work.