Find difference between two sets of records - sql

Question

I have a set of data on sql server something like:
ID ID_Invoice Article Quantity Status
1 10 carrot 10 null
2 10 carrot 5 C
3 10 onion 8 null
4 10 onion 4 C
5 11 tomato 20 null
6 11 tomato 18 C
7 11 onion 2 null
8 11 onion 1 C
It means that a customer ordered 10 carrots and 8 onions (on one invoice) but actually received only 5 carrots and 4 onions. If status is null then it is original quantity, if status is C then it is corrected quantity
I need to generate a table like
ID ID_Invoice Article Quantity
1 10 carrot -5
2 10 onion -4
3 11 tomato -2
4 11 onion -1
which shows the difference between ordered quantity and real quantity on each invoice. I have no idea how to begin. Any help deeply appreciated :)

Answer 1

Option with simple CASE expression without excessive JOIN
SELECT ID_Invoice, Article,
SUM(CASE WHEN Status IS NULL
THEN -1 * Quantity ELSE Quantity END) AS Quantity
FROM dbo.test38
GROUP BY ID_Invoice, Article
Result:
ID_Invoice Article Quantity
10 carrot -5
10 onion -4
11 onion -1
11 tomato -2
Demo on SQLFiddle

Answer 2

Least resource intensive:
SELECT id_invoice
, article
, org_quantity
, new_quantity
, new_quantity - org_quantity diff
FROM (SELECT id_invoice
, article
, max(CASE WHEN status IS NULL THEN quantity else null END) org_quantity
, max(CASE WHEN status = 'C' THEN quantity else null END) new_quantity
FROM orders
GROUP BY id_invoice
, article)
See it working here: http://sqlfiddle.com/#!4/f96adf/14

Answer 3

You didn't specify, which RDBMS you're using, but my answer is ANSI-SQL standard compliant :) Works with every valid RDBMS out there.
SELECT
yt1.ID_Invoice,
yt1.Article,
yt2.Quantity - yt1.Quantity AS Quantity
FROM
yourTable yt1
INNER JOIN yourTable yt2 ON yt1.ID_Invoice = yt2.ID_Invoice
AND yt1.Article = yt2.Article
AND yt2.Status = 'C'
WHERE
yt1.Status IS NULL
This answer is asuming, there's always a record with Status NULL and corresponding row with status 'C'. If this is not the case, you'd have to adjust it like this:
SELECT
yt1.ID_Invoice,
yt1.Article,
CASE WHEN yt2.Quantity IS NULL THEN yt1.Quantity ELSE yt2.Quantity - yt1.Quantity END AS Quantity
FROM
yourTable yt1
LEFT JOIN yourTable yt2 ON yt1.ID_Invoice = yt2.ID_Invoice
AND yt1.Article = yt2.Article
AND yt2.Status = 'C'
WHERE
yt1.Status IS NULL

Answer 4

So first of all you have to separate the actual from the ordered by making 2 queries and then you have to left join the orders to the actual .. something like this
select
Recived.ID,
Recived.ID_Invoice,
Recived.Article,
Recived.Quantity - Ordered.Quantity as Quantity
from
(select * from dataTable where Status is null) as Ordered
left join (select * from dataTable where Status = 'C') as Recived on (Ordered.ID_Invoice = Recived.ID_Invoice and Ordered.Article = Recived.Article )
NOTE! you will be better if you have an id for each article to use in the "left join" instead of comparing varchars.
Here is a fiddle example: http://sqlfiddle.com/#!2/16666/1