Data comparision across groups

Question

Hi,
create table Date_Cmp
"F1" numeric(4, 0),
"F2" varchar(10),
"F3"           date
begin
     insert into Date_Cmp(F1, F2, F3)
     values(1234, 'G2', to_date('05-Nov-2008 5:20AM', 'dd-mon-yyyy hh:miam'));
     insert into Date_Cmp(F1, F2, F3)
     values(1234, 'G1', to_date('05-Nov-2008 6:10AM', 'dd-mon-yyyy hh:miam'));
     insert into Date_Cmp(F1, F2, F3)
     values(1234, 'G2', to_date('05-Nov-2008 6:20AM', 'dd-mon-yyyy hh:miam'));
     insert into Date_Cmp(F1, F2, F3)
     values(1234, 'G1', to_date('06-Nov-2008 2:10AM', 'dd-mon-yyyy hh:miam'));
     insert into Date_Cmp(F1, F2, F3)
     values(1234, 'G2', to_date('06-Nov-2008 3:15AM', 'dd-mon-yyyy hh:miam'));
end;
select * from Date_Cmp
-- METHOD 1
select a.F1, min(a.F3) from
(select * from Date_Cmp
where F2 in ('G2')) a,
(select * from Date_Cmp
where F2 in ('G1')) b
where a.F1 = b.F1 and
a.F3 > b.F3
group by a.F1
-- METHOD 2
select F1, min(case when F2 in ('G2') then F3 else null end) as D1
from Date_Cmp
group by F1
having min(case when F2 in ('G2') then F3 else null end) > min(case when F2 in ('G1') then F3 else null end)
-- METHOD 3
select F1, min(case when F2 in ('G2') then F3 else null end) as D1
from Date_Cmp
group by F1
having count(case when F2 in ('G2') then F3 else null end > case when F2 in ('G1') then F3 else null end) > 0
-- METHOD 4
select F1, F2, F3, MIN(case when F2 = 'G2' then F3 else null end > case when F2 = 'G1' then F3 else null end) over (partition by F1, F2 order by F1, F2) as D1
from Date_Cmp
In the above data, I want to fetch the F3 date value when 'G2' record crosses over 'G1',
that is '05-Nov-2008 6:20AM'
It can be done easily as given in Method 1. Since, we handle large amount of data, we
cannot afford to do self-join. We want to get this done through a single recordset,
that is without using multiple in-line views.
Method 2 works well when the first record is deleted from the sample data,
that is F3 = '05-Nov-2008 5:20AM'. But, we cannot expect this always as
'G2' data may appear ahead of 'G1' as well.
Method 3 gives syntax error, even if it works, it would return the first row,
the wrong result as '05-Nov-2008 5:20AM'
Method 4 gives syntax error, if it get through, may give the expected result.
I am trying with other analytical functions to get the 1st F3 date on which G2
moves ahead of G1.
Please give me your suggestions and alternatives to get this done through
different methods, thank you.
Regards,
DR

Answer 1

Hi Boniest,
I have provided below SELECT statements and the output I get,
select * from Date_Cmp
F1     F2     F3
1234     G2     11/5/2008 5:20:00 AM
1234     G1     11/5/2008 6:10:00 AM
1234     G2     11/5/2008 6:20:00 AM
1234     G1     11/6/2008 2:10:00 AM
1234     G2     11/6/2008 3:15:00 AM
select a.F1, min(a.F3) from
(select * from Date_Cmp
where F2 in ('G2')) a,
(select * from Date_Cmp
where F2 in ('G1')) b
where a.F1 = b.F1 and
a.F3 > b.F3
group by a.F1
F1, MIN(A.F3)
1234, 11/5/2008 6:20:00 AM
I am exploring further to see what could be the problem, thank you.
Regards,
DR