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Bind Peeking only for "known" columns?

fjfrankenJan 14 2015 — edited Jan 15 2015

Hi all,

We are working on our 11.2.0.3 RAC (on AIX 7.1) database on trying to figure out why a certain repeated query ( batch load) is not using the correct execution plan.

The query itself looks like:

select CATENTRY_ID from CATENTRY where ((PARTNUMBER=:1 ) OR ((0 = :2 ) AND (PARTNUMBER IS NULL))) and ((MEMBER_ID=:3 ) OR ((0 = :4 ) AND (MEMBER_ID IS NULL)));

This query is an IBM Webshere internal query, which therefore is unchangeable.

The table in question has an Index available on PARTNUMBER & MEMBER_ID

The execution plan however looks like

The execution plan of the above statement looks like:

Execution Plan

----------------------------------------------------------

0 SELECT STATEMENT Optimizer Mode=ALL_ROWS (Cost=2038 Card=1 Bytes=23)

1 0 TABLE ACCESS FULL WCSADMIN.CATENTRY (Cost=2038 Card=1 Bytes=23)

So a FTS scan is used where an Index-lookup would be expected.

The values passed to this query are e.g.:

:1 = XA-GED-1068849

:2 = 1

:3 = -6000

:4 = 1

With the part of the WHERE CLAUSE then having ((0=1) AND (PARTNUMBER IS NULL)) and the same for ((0=1) AND (MEMBER_ID IS NULL)) would result in an Index lookup.:

select

catentry_id

from catentry

where ( (partnumber = 'XA-GED-5702810')

  or ( (0 = 1)

  and (partnumber is null)))

and ( (member_id = -6000)

  or ( (0 = 1)

  and (member_id is null))) ;

Execution Plan

----------------------------------------------------------

0 SELECT STATEMENT Optimizer Mode=ALL_ROWS (Cost=3 Card=1 Bytes=23)

1 0 TABLE ACCESS BY INDEX ROWID WCSADMIN.CATENTRY (Cost=3 Card=1 Bytes=23)

2 1 INDEX UNIQUE SCAN WCSADMIN.I0000064 (Cost=2 Card=1)

Somewhere in the parsing of the query the optimizer does not have/use all the information needed to determine the correct plan, allthough the tracefile shows all values are captured correctly

I would expect that the optimizer would "PEEK" all available variables to determine the best execution plan.

It looks however that the two BINDs for the "0=:2" and "0=:4" are not "peeked" and therefore not used, which results in a Full Table Scan as the PARTNUMBER IS NULL and MEMBER_ID IS NULL are not skipped.

Can anyone confirm that only BINDs for "existing/real" columns are peeked??

And is this configurable ??

Thanks

FJ Franken
This post has been answered by Jonathan Lewis on Jan 14 2015
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Comments

BEDE

select distinct status,count(*) col1
,sum(
case
when reviwe_status='Y' then 1
else 0
end
) number_reviewed
from temp1
group by status
;

Frank Kulash

Hi,
SUM (CASE ...), as Bede showed, will work. You could also use COUNT (CASE ...), like this:

SELECT    status              -- or  LOWER (status) AS status
,         COUNT (*)  AS col1  -- or a more descriptive name, like number_total
,	  COUNT ( CASE
	  	      WHEN  review_status = 'Y'
		      THEN  'OK'
	  	  END
	  	)    AS number_reviewed
FROM      temp1
GROUP BY  status
ORDER BY  status  -- or whatever
;

If you really want to display 'open' and 'close' even though the table has 'Open' and 'Close', as you said, then you just need to change the first line.
In any event, you don't need "SELECT DISTINCT". The GROUP BY clause guarantees that status will be distinct in the output

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