'lag' works in normal SQL statement, but not when in a view (resolved)

Question

hi,
got a problem when using 'lag' in a view.
if i set up a select statement using 'lag' and execute it, all the results are correct.
when i stick the exact same select into a view, then the results for the 'lag' entries are not correct any more.
has anyone experienced this ?
any hints would be good.
thanks
Martin
using Oracle 10g Express
version 10.2.0.1.0
can not download the patch because i can not log into metalink - no CSI
setting to resolved.
Message was edited by:
user614086

Answer 1

Hi again,
I think the problem is more with your expectation of what LAG should be doing than with LAG itself.
LAG must calculate based on the result set, in your stand alone query that means what's left after the WHERE clause is applied.
In the view that means across all rows the view produces. THEN you apply the where clause to the calculated values. You can see this in the example below.
So what you'd need to do is define this view in a manner in which the WHERE clause won't make a difference to the logical window produced.
That would mean using some columns in the partition by clause and order by clause, or leaving the lag function outside the view.
create table test_lag (column1 number, column2 varchar2(10), column3 date);
insert into test_lag values (1, 'ONE', trunc(sysdate,'DD') - 1);
insert into test_lag values (2, 'TWO' trunc(sysdate,'DD') );
insert into test_lag values (3, 'THREE', trunc(sysdate,'DD') + 1);
insert into test_lag values (4, 'FOUR', trunc(sysdate,'DD') + 2);
commit;
create or replace view test_lag_v
as
select column1, column2, lag(column2, 1) over (order by column1 asc) AS laggery, lag(column1) over (order by column3 desc) as laggery_2
from test_lag;
ME_XE?select *
  2  from test_lag_v
  3  where column1 <> 3;
           COLUMN1 COLUMN2                        LAGGERY                                 LAGGERY_2
                 4 FOUR                           THREE
                 1 ONE                                                                            3
2 rows selected.
Elapsed: 00:00:00.50
ME_XE?
ME_XE?select *
  2  from test_lag_v;
           COLUMN1 COLUMN2                        LAGGERY                                 LAGGERY_2
                 4 FOUR                           THREE
                 3 THREE                          ONE                                             4
                 1 ONE                                                                            3
3 rows selected.
Elapsed: 00:00:00.68