… executed without scanning and sorting full result set, so it is important for it to use index – in this case index range scan will…. Index on date_created separately would still work. The good from performance standpoint (even though a bit ugly) will be UNION workaround… some extra filtering takes place so you need to scan more rows by index then requested by LIMIT. However if you’re…
Post: How is join_buffer_size allocated?
July 5, 2010 By 9 Comments
… use an index. This is because we know that the nested loop is effectively going to do a table scan on the inner table — it has to, because there’s no index. If the query joins… << 30; # 1GB select * from (select 1 union select 1) as x1 join (select 1 union select 1) as x2 join…. That should…
Post: Database access Optimization in Web Applications.
September 12, 2006 By 10 Comments
… only one row while may require to scan hundreds of thousands of rows (or index entries) to do so. Other common killer… different – even if you have index on domain it still can require a lot of rows scanned to provide result set. Such…’ve seen people trying to join all queries in single UNION (with padding to accommodate different types and number of columns…
Comment: Distributed Set Processing with Shard-Query
May 14, 2011 By 27 Comments
… 8401″. This also allows effective range scans on hash indexes since the range is treated as a union of equalities (think in sets…
