Re: sql Vs RLA to test existance

[Luis Rodriguez <luisro58@xxxxxxxxx>]

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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