I've got this hypothetical table:

id deptID subdeptID promo sku
001 A 123 --- 789
002 A --- xyz 789
003 A 123 --- 789

I want to report a summary of the table that groups identical rows and counts them. E.g. :

Dept subdeptID promo sku
A 123 --- (2)
A 123 xyz (1)

Would it be wiser to write a SELECT query to obtain the second table above (if it's feasible), or instead add a "hits" column that increments by '1' when a row containing data identical to an existing row is to be stored?