Question

So I would like to search for the max time in a column:

sqlite> SELECT max(strftime('%Y-%m-%d %H:%M',time)) FROM posts WHERE thread_id=123456;
2012-10-02 02:31

For each thread_id returned by this query:

sqlite> SELECT thread_id FROM threads WHERE out_of_date=0;
111
123
187
...

Then I would like to search for all threads whose last_post field don’t match the time field returned by the first query, and set the out_of_date field to 1:

sqlite> UPDATE threads SET out_of_date=1 WHERE thread_id=123456 AND last_post!='2012-10-02 02:31';

Problem is, I’m not too sure how I should go about combining these three separate queries. Any thoughts?

Answer 1

The below SQL should update the threads table correctly. It uses a correlated sub-query to combine the 1st and 3rd of your queries. This can then be combined with your 2nd query by adding it’s WHERE clause.

UPDATE threads T
SET out_of_date = 1
WHERE out_of_date = 0
    AND last_post != (
        SELECT MAX(strftime('%Y-%m-%d %H:%M',time))
        FROM posts
        WHERE thread_id = T.thread_id
    )
;