O Martin Marques έγραψε στις Sep 28, 2004 :
> I have a bunch of queries in a system I'm finishing, and I bumped with a
> question on performace.
> Which is the best way to solve this:
>
> I need to know if there is at least one row in the relation that comes from a
> determinated query. Which is the best way to do this:
>
> (a) Build the query with "SELECT * ..." and after executing the query see if
> numRows()>0
> (b) Build the query with "SELECT count(*) ...", fetch the row and see if
> count>0
You could also try
(c) SELECT exists (select 1 ... limit 1) and test the boolean value
in the one and only row returned, where "..." is your clause
as in (a),(b).
>
> I'm working with (a) because I see it better in performace, but I wanted to be
> sure the numRows() will actually give me the exact amount of rows (had some
> problems in the past with Informix).
>
> The aplication is written in PHP.
>
>
--
-Achilleus