Re: SQL Optimization

["Charles Wilt" <charles.wilt@xxxxxxxxx>]

Pete,

1) Use Visual Explain to see exactly what the query is doing.

2) often the IN predicate is replaced by the query engine with a join.
 This usually results in the same or better performance.

But you might try a CTE instead

with tbl as ( select pissnv from ppcs301 group by
 pissnv having sum(pipctf)>100)
select picode,pissnv,emlnam,emfnam,emmnam, decimal(pipctf/100,5,2)
 as tot from ppcs301,peis301 where pissnv=em# and
 emstat='Y' and pissnv in(select pissnv from tbl)
order by emlnam,emfnam,emmnam

and maybe get rid of the IN explicitly
with tbl as ( select pissnv from ppcs301 group by
 pissnv having sum(pipctf)>100)
select picode,pissnv,emlnam,emfnam,emmnam, decimal(pipctf/100,5,2)
 as tot from ppcs301,peis301, tbl where pissnv=em# and
 emstat='Y' and pissnv = tbl.pissnv
order by emlnam,emfnam,emmnam

Charles

On Wed, Jan 7, 2009 at 2:01 PM, Pete Helgren <Pete@xxxxxxxxxx> wrote:
> I have run into a situation where two sub second queries, when combined,
> became a 10 -20 minute monster and I am not sure why.
>
> Here is the SQL statement being executed:
>
> select picode,pissnv,emlnam,emfnam,emmnam, decimal(pipctf/100,5,2)
>  as tot from ppcs301,peis301 where pissnv=em# and
>  emstat='Y' and pissnv in(select pissnv from ppcs301 group by
>  pissnv having sum (pipctf)>100 ) order by emlnam,emfnam,emmnam
>
> This query runs in less than a second and produces 5555 records:
>
> select picode,pissnv,emlnam,emfnam,emmnam, decimal(pipctf/100,5,2)
>  as tot from ppcs301,peis301 where pissnv=em# and
>  emstat='Y'
>  order by emlnam,emfnam,emmnam
>
> This query (the subselect) runs in less than a second and produces 4
> records:
>
> select pissnv from ppcs301 group by
>  pissnv having sum(pipctf)>100
>
> When combined (as in the first statement) it will take 10 - 20 minutes
> to run, process millions of records and produce 8 results (which is
> correct).
>
> Obviously, I am doing something wrong because I assumed the result of
> these two queries would also be sub-second to run.  What did I do wrong?
>
> Thanks.
>
> Pete Helgren
>
>
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