Originally posted by tamilselvan
You can do one more test. Remove the group by and see how many rows are returned after the 2 tables join. That will give you good idea how much space is needed.
I don't think so -- the space requirement is related more to the size of the output from the grouping than it is to the number of ungrouped rows.

For example,

Code:
Select Sum(my_num)
From   table_with_million_rows
... is going to require very little sort space, right?