RE: SQL and host indicator

Birgitta,

I don't believe this is the case anymore.

From the "High Performance Data Access Methods" presentation Q&A by Dan Cruikshank, IBM and Elvis
Budimlic, CTI.

"Dan - No, the count(*) returns a derived column representing the total number of rows in the result
set based on row selection (ie WHERE or ON clause settings). If no filtering is provided then the
count can be obtained from the table object itself in a single IO.

Elvis - COUNT(*) and COUNT(specificColumn) are functionally the same, so there should be no
performance difference, nor have we ever observed a contrary case. In fact, SQE has a fast path for
COUNT usage with
no selection criteria (i.e. no WHERE clause). If you do have selection criteria, it is far more
important to ensure you have proper indexes to help query optimizer satisfy the selection criteria.

Dan - When and where to create an EVI depends mainly on your application
requirements. In my presentation I created an EVI to obtain a fast count."



Charles Wilt
--
Software Engineer
CINTAS Corporation - IT 92B
513.701.1307
wiltc@xxxxxxxxxx

-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-bounces@xxxxxxxxxxxx]
On Behalf Of BirgittaHauser
Sent: Monday, July 21, 2008 1:33 PM
To: 'RPG programming on the AS400 / iSeries'
Subject: AW: SQL and host indicator

Hi,

If not necessary, I'd not use a count(*), because all rows must be read.
If I only want to check if a row exists, I'll use the following SELECT
statement:

Clear wPrvFL;
Exec SQL Select '1' into :wPrvFl
From ....
Where ...
Fetch First Row Only;

--> If a row is found wPrvFl is set to *On, otherwise it will not be
changed.
--> The executions stops after the first row is found.
--> An index only access might be performed.

Mit freundlichen Grüßen / Best regards

Birgitta Hauser

"Shoot for the moon, even if you miss, you'll land among the stars." (Les
Brown)
"If you think education is expensive, try ignorance." (Derek Bok)
"What is worse than training your staff and losing them? Not training
them
and keeping them!"

-----Ursprüngliche Nachricht-----
Von: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-bounces@xxxxxxxxxxxx]
Im
Auftrag von David FOXWELL
Gesendet: Monday, July 21, 2008 17:56
An: RPG programming on the AS400 / iSeries
Betreff: SQL and host indicator


Hi all,

I just compiled this. I just wanted to ask if this a perfectly normal way
to
set an indicator with SQL.

Thanks



D wPrvFl S N

EXEC SQL

SELECT

CASE WHEN COUNT(*) > 0 THEN '1' ELSE '0' END INTO : wPrvFl

FROM etc
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