How would l write SQL to label quantities until they run out? - sql

Question

I would like to label quantities (in the quantity table) using the labels assigned (see label assignment table) until the quantity goes to 0. Then I know that I am done labeling that particular ID.
label assignment table is as follows:
ID | Label | Quantity
1 aaa 10
1 bbb 20
2 ccc 20
And my quantity table:
ID | Total Quantity
1 60
2 20
And I would like to get the following result:
ID | Label | Quantity
1 aaa 10 (read from reference table, remaining 50)
1 bbb 20 (read from reference table, remaining 30)
1 [NULL] 30 (no label in reference table, remaining 0)
2 ccc 20 (read from reference table, remaining 0)

Answer 1

You can do it with a simple JOIN and UNION operation so as to include 'not covered' quantities:
SELECT la.ID, la.Label, la.Quantity
FROM label_assignment AS la
INNER JOIN quantity AS q ON la.ID = q.ID
UNION
SELECT q.ID, NULL AS Label, q.TotalQuantity - la.TotalQuantity
FROM quantity AS q
INNER JOIN (
SELECT ID, SUM(Quantity) AS TotalQuantity
FROM label_assignment
GROUP BY ID
) AS la ON q.ID = la.ID AND q.TotalQuantity > la.TotalQuantity
Demo here

Answer 2

DECLARE #PerLabelQuantity TABLE(Id int, Label varchar(10), Quantity int);
INSERT INTO #PerLabelQuantity
VALUES (1, 'aaa', 10), (1, 'bbb', 20), (2, 'ccc', 20);
DECLARE #QuantityRequired TABLE(Id int, TotalQuantity int);
INSERT INTO #QuantityRequired
VALUES (1, 60), (2, 20);
SELECT t.Id,
CASE WHEN o.Overflowed = 1 THEN NULL ELSE t.Label END AS Label,
CASE WHEN o.Overflowed = 1 THEN t.QuantityStillNeeded
WHEN t.QuantityStillNeeded < 0 THEN t.Quantity + t.QuantityStillNeeded
ELSE t.Quantity END AS Quantity
FROM (
SELECT p.Id, p.Label, p.Quantity,
MAX(p.Label) OVER (PARTITION BY p.Id) AS LastLabel,
r.TotalQuantity - SUM(p.Quantity)
OVER (PARTITION BY p.Id
ORDER BY Label
ROWS UNBOUNDED PRECEDING) AS QuantityStillNeeded
FROM #PerLabelQuantity p
INNER JOIN #QuantityRequired r ON p.Id = r.Id) t
INNER JOIN (VALUES (0), (1)) o(Overflowed)
ON t.LastLabel = t.Label AND t.QuantityStillNeeded > 0 OR Overflowed = 0
WHERE t.QuantityStillNeeded > -t.Quantity; -- Remove this if you want labels with
-- 0 quantity used, but you'll need to tweak
-- the CASE expression for Quantity
The subquery calculates a set of used up labels and how many items remain afterward. If there is any quantity remaining after the last label, then we need to insert a row in the result set. To do this, I join on a two-element table but the join condition is only true when we are at the last label and there is quantity remaining. This is probably a confusing way to do this, and we could combine the UNION from George's answer with the subquery from mine to avoid this Overflow table.
Here's the changed (and probably preferable) query:
SELECT Id,
Label,
CASE WHEN QuantityStillNeeded < 0 THEN Quantity + QuantityStillNeeded
ELSE Quantity END AS Quantity
FROM (SELECT p.Id, p.Label, p.Quantity,
r.TotalQuantity - SUM(p.Quantity)
OVER (PARTITION BY p.Id
ORDER BY Label
ROWS UNBOUNDED PRECEDING) AS QuantityStillNeeded
FROM #PerLabelQuantity p
INNER JOIN #QuantityRequired r ON p.Id = r.Id) t
WHERE t.QuantityStillNeeded > -t.Quantity
UNION ALL
SELECT q.Id, NULL AS Label, q.TotalQuantity - la.TotalQuantity AS Quantity
FROM #QuantityRequired AS q
INNER JOIN (
SELECT Id, SUM(Quantity) AS TotalQuantity
FROM #PerLabelQuantity
GROUP BY Id) la ON q.ID = la.ID
WHERE q.TotalQuantity > la.TotalQuantity

Answer 3

Simplest answer I think, after getting ideas from the other answers: Just create a "FAKE" label for the missing amount:
DECLARE #PerLabelQuantity TABLE(Id int, Label varchar(10), Quantity int);
INSERT INTO #PerLabelQuantity
VALUES (1, 'aaa', 10), (1, 'bbb', 20), (2, 'ccc', 20);
SELECT *
FROM #PerLabelQuantity
DECLARE #QuantityRequired TABLE(Id int, TotalQuantity int);
INSERT INTO #QuantityRequired
VALUES (1, 60), (2, 20);
SELECT *
FROM #QuantityRequired
-- MAKE A FAKE LABEL LET'S CALL IT [NULL] WITH THE AMOUNT THAT IS NOT LABELED
-- i.e. WITH THE REMAINING AMOUNT
-- Probably should be done by copying the original data and the following
-- into a temp table but this is just for proof of concept
INSERT INTO #PerLabelQuantity( Id, Label, Quantity )
SELECT q.ID,
NULL,
ISNULL(q.TotalQuantity - p.TotalQuantityLabeled, q.TotalQuantity)
FROM #QuantityRequired q
LEFT JOIN (SELECT p.ID, SUM(Quantity) AS TotalQuantityLabeled
FROM #PerLabelQuantity p
GROUP BY p.Id) p ON
p.ID = q.ID
AND q.TotalQuantity - p.TotalQuantityLabeled > 0
SELECT *
FROM #PerLabelQuantity p