Re: Varying fields and SQL predicate LIKE

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

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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.