quick ? : mysql duplicate row data vs adding hits col.

[mgm_03]

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?

TIA...

[r937]

select Dept 
     , subdeptID 
     , promo 
     , count(*) as hits
  from hypothetical 
group
    by Dept 
     , subdeptID 
     , promo

[mgm_03]

Thank you....being just a meager web developer I did not know I could GROUP By multiple columns (or if I did, it was forgotten).