Re: sql Vs RLA to test existance

Sean,

I read the original requirement as checking the existence of Table1 records
in Table2. So, if Table1 has more than one record that satisfies the
existence check in Table2, fetch would limit the number of Table1 records
read.

Now, I realize that the requirement seems to be a lot simpler than what I
initially thought, ie., just one table, so my suggestion would not apply...

Regards,

Luis Rodriguez
IBM Certified Systems Expert — eServer i5 iSeries
--



On Tue, Feb 15, 2011 at 11:30 AM, McGovern, Sean <Sean.McGovern@xxxxxxxxxxxx

wrote:

There is no need to have EXISTS and the FETCH FIRST ROW ONLY together,
they will both give the same result (and performance will be similar).
To me, it just confuses the requirement.



-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of Luis Rodriguez
Sent: 15 February 2011 15:31
To: RPG programming on the IBM i / System i
Subject: Re: sql Vs RLA to test existance

Of course, you can limit the SELECT further by using FETCH:

SELECT * FROM TABLE1 WHERE EXISTS(SELECT 1 FROM TABLE2 WHERE
TABLE1.FIELD
= TABLE2.FIELD)
FETCH FIRST ROW ONLY
;


Regards,

Luis Rodriguez
IBM Certified Systems Expert - eServer i5 iSeries
--



On Tue, Feb 15, 2011 at 10:44 AM, Luis Rodriguez <luisro58@xxxxxxxxx>
wrote:

In the SQL vs RLA contest, if you are using the SQL example below just

for

checking records, RLA should win in performance, as the process of
Validating the query, optimizing it (creating an Access Plan) building

the

ODP, etc is very expensive in time terms, compared to a simple CHAIN,

where

practically the only overhead is when you OPEN the file.

Regards,
Luis Rodriguez
IBM Certified Systems Expert - eServer i5 iSeries
--



On Tue, Feb 15, 2011 at 10:27 AM, Luis Rodriguez

<luisro58@xxxxxxxxx>wrote:

David,

IIRC, EXISTS stops as soon as it finds the first record. The syntax

is:

SELECT * FROM TABLE1 WHERE EXISTS(SELECT 1 FROM TABLE2 WHERE
TABLE1.FIELD = TABLE2.FIELD) ;

Regards,
Luis Rodriguez
IBM Certified Systems Expert - eServer i5 iSeries
--




On Tue, Feb 15, 2011 at 10:14 AM, David FOXWELL

<David.FOXWELL@xxxxxxxxx>wrote:

Hi,

I need to find if a transaction of a particular type and amount

exists

for a client.

I cannot remember how to apply the SQL Exists( ) to look for the
transaction.

Select '1' from ???? where exists ( select * from mytable where

myfield =

'myfield')


Then again, I seem to remember that EXists will scan all the rows

and not

just stop at the first one that satisfies the search criteria as I

could do

with RLA.

Can someone put me straight please?

Thanks.

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