Need Help in analytic function (LAG)

Question

The requirement is like I have a table with belwo colums
col1 count flag flag2
abc 1 Y Y
xyz 1 Y Y
xyz 1 Y NULL
xyz *2* N N
xyz 2 Y NULL
def 1 Y Y
def 1 N NULL
To get the flag2 columns
1.Assign falg2 as flag for rownum=1
2. We have to check the colm1,count of current row with colm1,count of previous row .if the colm1 and cnt are same then we have to assign null...
Below is the query i used to get the flag2 values
SELECT colm1,count,flag
CASE WHEN
LAG(count, 1,null) OVER (PARTITION BY colm1 ORDER BY colm1 DESC NULLS LAST) IS NULL
and LAG(flag, 1, NULL) OVER (PARTITION BY colm1 ORDER BY colm1,cycle DESC NULLS LAST) IS NULL
THEN flag
END AS flag2
FROM table1
but the above query returns the below o/p which is wrong
col1_ count flag flag2
abc 1 Y Y
xyz 1 Y Y
xyz 1 Y NULL
xyz *2* N NULL
xyz 2 Y NULL
def 1 Y Y
def 1 N NULL
Thanks
Edited by: user9370033 on Apr 8, 2010 11:25 PM

Answer 1

Well, you haven't quite explained your full requirement in this
1.Assign falg2 as flag for rownum=1
2. We have to check the colm1,count of current row with colm1,count of previous row .if the colm1 and cnt are same then we have to assign null...as you don't say what flag2 should be set to if com1 and cnt are not the same as the previous row.
but how about this as my first guess what you mean...
SQL> with t as (select 'abc' as col1, 1 as cnt, 'Y' as flag from dual union all
  2             select 'xyz', 1, 'Y' from dual union all
  3             select 'xyz', 1, 'Y' from dual union all
  4             select 'xyz', 2, 'N' from dual union all
  5             select 'xyz', 2, 'Y' from dual union all
  6             select 'def', 1, 'Y' from dual union all
  7             select 'def', 1, 'N' from dual)
  8  -- END OF TEST DATA
  9  select col1, cnt, flag
10        ,case when lag(col1) over (order by col1, cnt) is null then flag
11              when lag(col1) over (order by col1, cnt) = col1 and
12                   lag(cnt) over (order by col1, cnt) = cnt then null
13              else flag
14         end as flag2
15  from t
16  /
COL        CNT F F
abc          1 Y Y
def          1 Y Y
def          1 N
xyz          1 Y Y
xyz          1 Y
xyz          2 Y Y
xyz          2 N
7 rows selected.
SQL>