On Jul 13, 2008, at 11:37 AM, Igor Tandetnik wrote: >> >> Does this change if I have an ORDER BY clause that does >> not match any index? > > No (though it would take longer to get the first row, as SQLite will > have to retrieve and sort all the records first).
If a query has both a LIMIT and an ORDER BY and the ORDER BY is such that a sort is required (in other words there is no index that can be used to satisfy the ORDER BY) then SQLite implements the sort using a priority queue. As each (unsorted) row comes out of the original query, that row is placed into the queue in order (using a O(logN) insertion). But if the LIMIT is K then only the first K elements of the queue are retained. So the sorting process is still O(NlogN) but because elements beyond the Kth element are discarded, less temporary memory and/or disk space is used to do the sort. So there is potentially some memory savings from specifying a LIMIT with an ORDER BY but the computation time is roughly the same with or without the LIMIT. The query still must compute the entire result set before it outputs the first row. D. Richard Hipp [EMAIL PROTECTED] _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
