Conditional GROUP BY clause

Question

Hi,
I have four columns in group by clause. I want to add conditional group by clause.
Case 1 : If one of the  column's value is null, I don't want to include it in group by clause. Means, Now GROUP BY clause will have only 3 columns.
Case 2 : If not null, then GROUP BY clause with all four columns.
Please help me out on this.
Thanks in advance.  

Answer 1

Hi
I think it won't matter, all group functions by default ignore NULLs so your result won't differ.
select  dept, loc, sum(sal)
from (
select 'A' emp , 1 dept , 'P' loc , 100 sal from dual union all
select'B',1,'P',200 from dual union all
select'C',2,'P',300 from dual union all
select'D',2,'P',400 from dual union all
select'E',3, 'P',500 from dual union all
select'F',3, 'P',600 from dual union all
select'G',4, 'Q',700 from dual union all
select'H', null,'Q' , 1000 from dual union all
select'I',null ,'Q', 2000 from dual union all
select 'J' ,null, 'Q',300 from dual)
group by dept,loc;
Output
DEPT      LOC      SUM(SAL)
1                P      300
2                P      700
3                P      1100
                Q      3300
4                Q      700
Now by doing grouping only for NOT NULL values,
select dept,loc, sum(sal)
from (
select 'A' emp , 1 dept , 'P' loc , 100 sal from dual union all
select'B',1,'P',200 from dual union all
select'C',2,'P',300 from dual union all
select'D',2,'P',400 from dual union all
select'E',3, 'P',500 from dual union all
select'F',3, 'P',600 from dual union all
select'G',4, 'Q',700 from dual union all
select'H', null,'Q' , 1000 from dual union all
select'I',null ,'Q', 2000 from dual union all
select 'J' ,null, 'Q',300 from dual)
where dept is not null          --------------NOT NULL Condition
group by dept, loc;
Output
DEPT     LOC      SUM(SAL)
1           P           300
2           P           700
3           P           1100
4           Q           700
Now by doing grouping only for NULL values,
select dept,loc, sum(sal)
from (
select 'A' emp , 1 dept , 'P' loc , 100 sal from dual union all
select'B',1,'P',200 from dual union all
select'C',2,'P',300 from dual union all
select'D',2,'P',400 from dual union all
select'E',3, 'P',500 from dual union all
select'F',3, 'P',600 from dual union all
select'G',4, 'Q',700 from dual union all
select'H', null,'Q' , 1000 from dual union all
select'I',null ,'Q', 2000 from dual union all
select 'J' ,null, 'Q',300 from dual)
where dept is null               --------------NULL Condition
group by dept, loc;
Output
DEPT      LOC         SUM(SAL)
                Q           3300
The output is same for both the conditions.