Re: SQL - EXISTS

[Javier Sanchez <javiersanchezbarquero@xxxxxxxxx>]

Mark, this is very close to it.  Thanks.

El mié, 23 nov 2022 a las 1:18, Mark Waterbury (<
mark.s.waterbury@xxxxxxxxxxxxx>) escribió:

> Alan,
>
> You should NOT do a "SELECT * ..." if you want better performance.
>
> You can do this "existence" checking like this:
>
>     EXISTS ( SELECT 1 FROM EMPLOYEE WHERE SALARY > 60000
>             FETCH FIRST 1 ROWS ONLY )
>
> I learned this trick from this article:
>     https://www.seg.de/2012-10-existence-check-sql-through-the-ages/
>
> Even though it is not specific to Db2i, it is for "Db2" ... interesting to
> learn how improving the performance of such "existence" checks has improved
> over the years.
>
> Hope that helps ...
>
> Mark S. Waterbury
>
>
>
> On Tuesday, November 22, 2022 at 03:50:24 PM EST, Alan Cassidy <
> cfuture@xxxxxxxxxxx> wrote:
>
>
>
>
>
> SQL references gives an example of EXISTS:
>
> EXISTS (SELECT *
>     FROM EMPLOYEE WHERE SALARY > 60000)
>
> I would assume that the search in file EMPLOYEE stops when it finds the
> first instance of a row that matches.
>
> Is that so?
>
> I'm asking because I'm modifying a program that has a /very/ /heavy/
> performance burden, and I have to squeeze milliseconds out of it
> anywhere I can get it.
>
> --Alan Cassidy
>
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