SQL SERVER, ORACLE - How use conditional logic in select, case statement

Prevention zero divide error:

select b.inventlocationid, itemid, a.availphysical, a.postedqty, 
a.postedvalue / case 
                  when a.postedqty = 0 then 1 
                  else a.postedqty 
                end as cost_avg_mj
from inventsum a
join inventdim b
on b.inventdimid = a.inventdimid and
b.dataareaid = a.dataareaid
where
a.itemid like 'S-%' and
a.availphysical <> 0