Re: Providing an alternative result when there is no result

Merlin Moncure <mmoncure@gmail.com> writes:
> On Mon, May 18, 2009 at 3:13 PM, Joshua Berry <yoberi@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