Re: SQL - EXISTS

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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