On Sun, Apr 7, 2013 at 9:08 AM, Baruch Burstein <bmburst...@gmail.com>wrote:
> If I issue a select statement with a ORDER BY clause and a LIMIT clause, > does SQLite do a full sort (assuming no index) and then return the first X > rows, or just a partial sort to get the first X sorted results? > It uses a btree as a priority queue. If you have LIMIT N, then it initially starts putting results into the btree until the btree contains N entries. Then for each additional row, it first adds the value to the btree, then removes the largest entry in the btree. Hence the btree always holds the smallest N entries seen so far. Once all is finished, it walks the btree to output the results. So with limit N, it never stores more than N results at one time. -- D. Richard Hipp d...@sqlite.org _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
