Query help, subtract two query parts

Question

Hi,
I am beginner of PL/SQL and have a problem I couldn’t solve:
Table (op_list):
Item     -     Amount -     Status
Item1     -     10     -     in
Item2     -     12     -     in
Item3     -     7     -     in
Item1     -     2     -     out
Item2     -     3     -     out
Item1     -     1     -     dmg
Item3     -     3     -     out
Item1     -     2     -     out
Item2     -     5     -     out
Item2     -     2     -     in
Item3     -     1     -     exp
Would like to get result of query (subtract amount of 'out/dmg/exp' from 'in' ):
Item - Amount left
Item1     -     5
Item2     -     6
Item3 -     3
I wrote code that returns sum of all incoming items and sum all out/dmg/exp items, but couldn’t solve how to subtract one part of querry from another. Or maybe there is a better way. Also worried what happens if there is no 'out/dmg/exp' only 'in'
select item.name, sum(op_list.item_amount)
from op_list
inner join item
on op_list.item = item.item_id
where op_list.status = 'in'
group by item.name
union
select item.name, sum(op_list.item_amount)
from op_list
inner join item
on op_list.item = item.item_id
where op_list.status = 'out'
or op_list.status = 'dmg'
or op_list.status = 'exp'
group by item.name
Return:
Item1     -     10      [10 in]
Item1     -     5     [2+1+2]
Item2     -     14     [12+2]
Item3     -     7
Item3     -     4     [3+1]
Thanks in advance

Answer 1

Hi,
We can also use simple inline views to get what we need.
select a.item,a.amount-b.amount Balance from
(select item,sum(amount) Amount from op_list
where status = 'in'
group by item) a,
(select item,sum(amount) Amount from op_list
where status in ('out','dmg','exp')
group by item) b
where
a.item=b.item
order by item;
ITEM       BALANCE
Item1                      5
Item2                      6
Item3                      3Regards,
Prazy