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Eric,

Thanks for the info, I personally prefer using the ON join for filtering
also. I like the syntax better in that it keeps the join/filter fields with
the related file, but had never thought that it might be a better performer.

Duane Christen

-----Original Message-----
From: DeLong, Eric [mailto:EDeLong@xxxxxxxxxxxxxxx]
Sent: Friday, November 11, 2005 9:17 AM
To: 'RPG programming on the AS400 / iSeries'
Subject: RE: Returning Values from two different Tables


Duane,

I've noticed similar performance improvements when using CTE constructs.  I
suppose I always assumed that the CTE expressions were faster because it
potentially reduces the number of rows to process, which allows the joins to
process faster.  I generally use CTE to pre-summarize sales data before
producing report data...

with SlsCy (Cust, Sales, Cost, TrnCnt) as (
        Select Cst#, sum(Extd-Disc), sum(Cost), count(distinct order#)
        from saleshist where tdate >= '2005-10-01' and tdate <= '2005-10-31'
),
     SlsLy (Cust, Sales, Cost, TrnCnt) as (
        Select Cst#, sum(Extd-Disc), sum(Cost), count(distinct order#)
        from saleshist where tdate >= '2004-10-01' and tdate <= '2004-10-31'
)

/* Show all current-year customers, with their sales from last year.... */

Select SlsCy.Cust, SlsCy.Sales, SlsLy.Sales ....
>From SlsCy                                             left outer join 
     SlsLy on (SlsCy.Cust=SlsLy.Cust)

Union All

/* Now, add in the customers with sales last year, but not this year.......
*/

Select SlsCy.Cust, SlsCy.Sales, SlsLy.Sales ....
>From SlsLy                                             exception join 
     SlsCy on (SlsCy.Cust=SlsLy.Cust)



(I wish DB2/400 supported full join......)

A similar benefit seems to occur when you move filtering in a join statement
from the Where clause into the ON join criteria.  It's particularly
noticable when joining very large files into a summary result set, such as
for a dashboard sales report.  



Eric DeLong
Sally Beauty Company
MIS-Project Manager (BSG)
940-297-2863 or ext. 1863





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