Merlin Moncure <mmonc...@gmail.com> writes:
> On Mon, May 18, 2009 at 3:13 PM, Joshua Berry <yob...@gmail.com> wrote:
>> Is there an easy and efficient way to return a boolean false for a query
>> that returns no result, and true for one that does return a result?
> Probably the best general approach is to:
> select count(*) = 1 from
> (
> <query> limit 1
> )q;
Seems like EXISTS() is much more straightforward ...
> the point being that in some cases (not all obviously) the limit 1 can
> be a huge win, as you only care if there are rows or not.
... the system does know about optimizing EXISTS as if it were a LIMIT
query; you don't need to tack that on yourself.
regards, tom lane
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