Re: Varying fields and SQL predicate LIKE

["Carel Teijgeler" <coteijgeler@xxxxxxxxx>]

Should the LOCATE function not be considered? Something like (not really
sure about the correct syntax):

WHERE LOCATE(street, 'MAIN') > 0

With regards,
Carel Teijgeler

*********** REPLY SEPARATOR  ***********

On 22-7-2010 at 10:07 CRPence wrote:

> On 22-Jul-2010 08:12, Charles Wilt wrote:
> > I've got a 3.1 million row table with a 25 character field that holds a
street address, ex. '123 MAIN ST.'
> > We currently perform seraches by address like so:
> >   select * from myTable where address like '%MAIN%'
> >
> > Given the leading '%', I know the search will require a full table
(perhaps full index) scan.
> > Given that the average TRIM'd length of the data in the field is 16 and
that RPG works much faster with varying fields. I was
> > thinking that if I changed the field to varying, the DB wouldn't have
any trailing blanks to compare too and thus my searches
> > should be about 36% faster...
> >
> > However, I'm not seeing a 36% improvement. In fact, it appears that
performance is worse by a couple of percent!
> >
>
>   Since a blank is not the prefix of the data being searched, you could
not see the maximum potential improvement you are looking for. 
>  Try searching on '% MAIN%' instead, to effect a better test; not that I
trust the performance test results for both non-dedicated and 
> without averaged repeated tests including reversed order of any two
compared scenarios.
>   By the way, also try ALLOCATE(0) [or whatever syntax has that effect]
to force all of the data into its own segment.  Depending on 
> optimization, at the LIC DB level that storage could be the best possible
means to reduce the I\O; the I\O is the greatest impediment 
> for completing the processing the quickest.  If the query has the
capability to interrogate only the AuxSID, that could be similar to 
> an index-only access, whereby all of the processed data is effectively
contiguous.