Question

I have a log for documents that go through my application. The log looks like this:

TABLE: log
==================================================
| log_id | document_id | status_code | timestamp |
==================================================
| 1      | 10          | 100         | 12345     |
--------------------------------------------------
| 2      | 10          | 200         | 23456     |
--------------------------------------------------

I need a list of document_id that have been “stuck” in a certain status_code for a given duration (say 10 minutes; timestamp is Unix timestamp, btw). If a particular document_id is “stuck” in a certain status_code, that status_code will be the last status_code for that document_id.

How do I query this? The 2 things I’m not sure of:

1. How do I check if the document has been in a certain status for a certain period of time? I’m guessing I can use some sort of function/formula in my SQL (e.g. now – 10 minutes), but I don’t know how to do that.
2. How do I check the duration of only the last status code?

Answer 1

SELECT log.document_id
     , (UNIX_TIMESTAMP() - log.timestamp) / 60
       AS MinutesSinceLastChange 
FROM log
  JOIN
    ( SELECT document_id
           , MAX(timestamp) AS last_change
      FROM log
      GROUP BY document_id
      HAVING (last_change < (UNIX_TIMESTAMP() - 60 * 10))  <-- that is 10 minutes
    ) AS grp
    ON  grp.document_id = log.document_id
    AND grp.last_change = log.timestamp
WHERE log.status_code = "200"             <-- code you want to check