difference of sums of two different tables in sql

Question

I have two sql tables, purchase and sent , I want to know the outstanding balance of items at any date. For this I am trying to take sum(puchase.quantity) - sum(sent.quantity) where date<some date . I can have individual queries but I dont know how to combine them.

Here are individual queries:

select item,sum(quantity) from sent where datee <'some date' group by item
select item,sum(quantity) from purchase where datee<'some date' group by item

Please tell me if there is aa better way to get the outstanding balance.

Thanks in advance.

Answer 1

I think you want this

Here is working demo SQLFiddle

CREATE TABLE sent
(
item int,
quantity int
);

CREATE TABLE purchase
(
item int,
quantity int
);

insert into sent values(1,4);
insert into sent values(2,7);
insert into sent values(3,9);
insert into sent values(4,5);
insert into sent values(5,9);

insert into purchase values(1,2);
insert into purchase values(2,5);
insert into purchase values(3,3);
insert into purchase values(4,2);
insert into purchase values(5,7);


select sent.item , (sum(IFNULL(sent.quantity,0)) - sum(IFNULL(purchase.quantity,0))) as diff 
FROM sent  , purchase Where sent.item = purchase.item group by sent.item

Answer 2

Maybe there's a more succint way to get what you want, but the folliwing should give you correct results:

SELECT s.item, 
        s.qty as total_sent, 
        COALESCE(p.qty,0) as total_purchase, 
        s.qty - COALESCE(p.qty,0) as stock
FROM 
(
  SELECT item, sum(quantity) as qty
  FROM sent 
  GROUP BY item
) s
LEFT JOIN 
(
  SELECT item, sum(quantity) as qty
  FROM purchase
  GROUP BY item
) p
ON p.item = s.item