Any difference between distinct and aggregate function in sql query cost???

Question

Hi,
I have executed many sql stmts patterns- such as:
a) using a single table
b) using two tables, using simple joins or outer joins
but i have not noticed any difference in sql stmts in cost and in execution plan....
Anyway, my colleague insists on that using aggregate function is less costly compared to
distinct....(something i have not confirmed, that's why i beleive that they are exactly the same...)
For the above reffered 1st sql pattern.. we could for example use
select distinct deptno
from emp
select count(*), deptno
from emp
group by deptno select distinct owner, object_type from all_objects
select count(*), owner, object_type from all_objects
group by owner, object_typeHave you found any difference between the two ever...????
Note: I use Ora DB 10g v2.
Thank you,
Sim

Answer 1

distinct and aggregate function are for different uses and may give same result but if u r using aggregate function to get distinct records, it will be expensive...
ex
select distinct deptno from scott.dept;
Statistics
0 recursive calls
0 db block gets
2 consistent gets
0 physical reads
0 redo size
584 bytes sent via SQL*Net to client
488 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
4 rows processed
select deptno from scott.emp group by deptno;
Statistics
307 recursive calls
0 db block gets
60 consistent gets
6 physical reads
0 redo size
576 bytes sent via SQL*Net to client
488 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
6 sorts (memory)
0 sorts (disk)
3 rows processed
Nimish Garg
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