SQL & PL/SQL

hi gems..good afternoon..

I read that the COUNT() function always returns 0 (zero) if there is no matching rows in the table.

The following code returns the 0 as expected:

SELECT COUNT(1) FROM book_table
             WHERE client_id = 10009
               AND book_id = 5465465
               AND book_sub_id = 'gfdf'
               AND amount = 78686

But when I used the GROUP BY clause with the query, then it returned nothing:

SELECT COUNT(1) FROM book_table
             WHERE client_id = 10009
               AND book_id = 5465465
               AND book_sub_id = 'gfdf'
               AND amount = 78686
group by client_id,book_id,book_sub_id,amount

Why this is happening..please suggest...