SQL: sum(unit) table a minus sum(unit) table b

Question

I have 2 tables;

1. item_in(item_id,unit)
2. item_out(item_id,unit)

Now let say I want to know how many unit is being insert for every item, I just query

select sum(unit) from item_in order by item_id

Likewise, if I want to know how many unit is being taken out, I just query

select sum(unit) from item_out order by item_id

I don't know how to query the balance (item_in - item_out) for each item.

It is great if I can make all the query in one stored procedure, because I want to call the procedure using DataWindow.

Please help, thank you.

Answer 1

SELECT
  item_id,
  SUM(unit) AS unit_balance
FROM (
  SELECT item_id, unit FROM item_in
  UNION ALL
  SELECT item_id, -unit FROM item_out
) AS s (item_id, unit)
GROUP BY item_id

Answer 2

I know nothing about sybase, but this, or a subtle variation of this, should work.

select t1.item_id, sum(t1.unit - coalesce(t2.unit, 0)) as Balance
from item_in t1
left join item_out t2
on t1.item_id = t2.item_id
group by t1.item_id

Coalesce will put a 0 whenever a unit from t2 is NULL, so that you can properly substract the item_in unit amount from it.

Note: This works in SQL Server. I don't know if you might find any syntactic difference when running it in sybase :(

Answer 3

i hope the following query works:

select 
sum(inn.unit) - sum(outt.unit)
from item_in inn
inner join item_out outt on inn.item_id = outt.item_id