Issue regarding rownum in sql query

Question

Hi All,
When I'm running the query below
select 'OP',
'ORG_CODE_PROVIDER',
rownum as ranking,
x.ORG_CODE_PROVIDER,
z.description,
x.value_count,
round(x.value_count / 200432, 4) * 100 as value_pct,
NULL as BATCH_KEY,
'9BED55A4328EFD71E040D20A143245E3' as BATCH_SET_KEY,
'OVERALL',
'OVERALL'
from (select ORG_CODE_PROVIDER, count(*) as value_count
from STAGING_TST.OP t
group by ORG_CODE_PROVIDER
order by count(*) desc, 1 asc) x,
(select code, description from ref_hd.MV_ORG_CODE_PROVIDER) z
where z.code(+) = x.ORG_CODE_PROVIDER
and rownum <= 10
it is showing me results based on the rownum of block x.
But when I try to insert these records in a table like
insert into QA_TST.OP_STAGE_COL_VAL_FREQ
select 'OP',
'ORG_CODE_PROVIDER',
rownum as ranking,
x.ORG_CODE_PROVIDER,
z.description,
x.value_count,
round(x.value_count / 200432, 4) * 100 as value_pct,
NULL as BATCH_KEY,
'9BED55A4328EFD71E040D20A143245E3' as BATCH_SET_KEY,
'OVERALL',
'OVERALL'
from (select ORG_CODE_PROVIDER, count(*) as value_count
from STAGING_TST.OP t
group by ORG_CODE_PROVIDER
order by count(*) desc, 1 asc) x,
(select code, description from ref_hd.MV_ORG_CODE_PROVIDER) z
where z.code(+) = x.ORG_CODE_PROVIDER
and rownum <= 10
On querying the table I'm getting totally different result based on the rownum governed by block y.
I could not able to understand why is it happening. Why oracle is not inserting the records that it is showing in select query.
Moreover, how can I fix this issue and get the desired result.
Thanks
Tarun

Answer 1

Hi,
Whenever you post any code, indent it so that how it looks on the screen reflects what it is doing. In particular, make it easy to see what are the sub-queries. Whenever you post formatted text (such as query results as well as code) on this site, type these 6 characters:
\(small letters only, inside curly brackets) before and after each section of formatted text, to preserve spacing.
I originally posted an inaccurate answer becuase I couldn't understand your unformatted code.
How ROWNUM is assigned in a join depends on how the optimizer chooses to perform the join.  If you want consistent results, then do the join first (in a sub-query), use ORDER BY clause in that sub-query, and use ROWNUM only in the parent query, which should not include a join.
The analytic ROW_NUMBER function is a lot more powerful and versatile than ROWNUM.  You might look into using it (though the extra power may not be needed in this particular problem).
Edited by: Frank Kulash on Feb 10, 2011 11:29 AM