Replace cursors with queries - sql

Question

Let's say I have a booking covering 6 hours and 3 discounts covering 2 hours each. I want to split my booking into 3 parts so I can allocate 2 hours per discount.
It would return something like this:
BookingId 1 | DiscountId 1 | Qty 2
BookingId 1 | DiscountId 2 | Qty 2
BookingId 1 | DiscountId 3 | Qty 2
I would then insert those records this into another table.
I'm using an heavily optimized query to determine the number of hours available for each discount. However, I can't find a "good" way to allocate my booking to each discount without using a cursor.
(...)
WHILE ##FETCH_STATUS = 0
BEGIN
IF #RequiredQty = 0
RETURN
IF #RequiredQty <= #AvailableQty
BEGIN
INSERT INTO discount.Usage (DiscountId, BookingId, Quantity)
VALUES (#DiscountId, #BookingId, #RequiredQty)
SET #RequiredQty = 0
END
IF #RequiredQty > #AvailableQty
BEGIN
INSERT INTO discount.Usage (DiscountId, BookingId, Quantity)
VALUES (#DiscountId, #BookingId, #AvailableQty)
SET #RequiredQty -= #AvailableQty
END
FETCH NEXT FROM ecursor INTO #DiscountId, #AvailableQty
END
DEALLOCATE ecursor
I tried building the corresponding query but I can't select and assign variables at the same time. Using a cursor is not really a problem (besides some potential performance issues) but I was just curious to see if with the newest SQL Server we can convert our old cursors to something better?
Thanks,
Seb

Answer 1

You can useCTE RECURSIVE to make a Table.
like this.
DECLARE #BookingId INT = 1;
DECLARE #RequiredQty INT = 2;
DECLARE #Hours INT = 7;
CREATE TABLE #T
(
BookingId INT,
DiscountId INT,
Quantity INT
)
;WITH CTE([Count],[Quantity],Rk) AS
(
SELECT
CASE
WHEN [HOURS] - #RequiredQty > #RequiredQty THEN #RequiredQty
ELSE [HOURS] - #RequiredQty
END ,
T.HOURS,1
FROM
(
SELECT #Hours [HOURS]
) AS T
UNION ALL
SELECT CASE
WHEN CTE.[Quantity] - #RequiredQty > #RequiredQty THEN #RequiredQty
ELSE CTE.[Quantity] - #RequiredQty
END AS [Count],
CTE.[Quantity] - #RequiredQty,
RK + 1
FROM CTE
WHERE CTE.[Quantity] - #RequiredQty > 0
)
INSERT INTO #T(BookingId,DiscountId,Quantity)
SELECT #BookingId,Rk,[Count] FROM CTE
option (maxrecursion 0)
select * from #T
SQLDEMO

Answer 2

This is another approach, but don't know if this code has better performance than cursor.
DECLARE #DiscountStocks TABLE (Id INT IDENTITY(1,1), DiscountId INT, LastQty INT)
INSERT INTO #DiscountStocks (DiscountId, LastQty) VALUES (1, 5)
INSERT INTO #DiscountStocks (DiscountId, LastQty) VALUES (2, 2)
INSERT INTO #DiscountStocks (DiscountId, LastQty) VALUES (3, 1)
DECLARE #DiscountBookings TABLE (Id INT IDENTITY(1,1), DiscountId INT, BookingId INT, Qty INT)
DECLARE #BookingDiscount TABLE (Id INT IDENTITY(1,1), BookingId INT, DiscountId INT, Qty INT)
INSERT INTO #BookingDiscount (BookingId, DiscountId, Qty) VALUES (1, 1, 4)
INSERT INTO #BookingDiscount (BookingId, DiscountId, Qty) VALUES (1, 2, 2)
INSERT INTO #BookingDiscount (BookingId, DiscountId, Qty) VALUES (1, 3, 1)
INSERT INTO #BookingDiscount (BookingId, DiscountId, Qty) VALUES (2, 1, 1)
INSERT INTO #BookingDiscount (BookingId, DiscountId, Qty) VALUES (2, 2, 2)
SELECT BD.Id AS BDId, DS.Id AS DSId, DS.LastQty, BD.Qty
, DS.LastQty - (SELECT SUM(Qty) FROM #BookingDiscount WHERE Id <= BD.Id AND DiscountId = BD.DiscountId) AS QtyAfterSubstract
INTO #LastDiscountStock
FROM #DiscountStocks DS
INNER JOIN #BookingDiscount BD ON DS.DiscountId = BD.DiscountId
ORDER BY BD.Id, DS.Id
INSERT INTO #DiscountBookings (DiscountId, BookingId, Qty)
SELECT DSId, BDId, Qty
FROM #LastDiscountStock
WHERE QtyAfterSubstract >= 0
DROP TABLE #LastDiscountStock
SELECT * FROM #DiscountBookings