* Bruce Momjian ([email protected]) wrote: > Thanks, TODO item readded with a clearer description: > > * Allow ORDER BY ... LIMIT 1 to select high/low value without sort or > index using a sequential scan for highest/lowest values > > Right now, if no index exists, ORDER BY ... LIMIT 1 requires we sort > all values to return the high/low value. Instead The idea is to do a > sequential scan to find the high/low value, thus avoiding the sort.
Could we take this perhaps a step further and consider things like
'LIMIT 10' and come up with an approximate point where the trade-off
exists? Actually, thinking about this a minute more perhaps there isn't
even a trade-off to be made... What you're suggesting is basically a
size-of-1 temporary memory structure for the 'sort'. Isn't there
already a memory structure used to perform the sorting though? Could it
be adjusted such that it's of a fixed size when 'LIMIT' is given, as
above?
Just some thoughts, while I think the specific 'LIMIT 1' case is
probably pretty common I think the 'LIMIT 10' or 'LIMIT 50' (or however
many you want to display on the webpage...) is a pretty common use case
too and it sounds like we could improve those too with this mechanism.
Thoughts?
Thanks,
Stephen
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