Iterate inserted in trigger - sql

Question

This SQL Server trigger works correctly for a single insert
CREATE TRIGGER [dbo].[DebitSale]
ON [dbo].[OrderDetails]
AFTER INSERT, UPDATE
AS
DECLARE #OrderId bigint
DECLARE #OrderNr int
DECLARE #TaxRate decimal(9,2)
DECLARE #Tax decimal(9,2)
DECLARE #Total decimal(9,2)
DECLARE #syncRate decimal(9,8)
DECLARE #Net decimal(9,2)
DECLARE #OldNet decimal(9,2)
DECLARE #ExactFee decimal(9,2)
DECLARE #Fee decimal(9,2)
DECLARE #JobId bigint
DECLARE #ItemCode nvarchar(35)
IF EXISTS ( SELECT 0 FROM inserted )
BEGIN
SELECT #syncRate = SyncRate
FROM dbo.[UserAccount]
WHERE Id = 0
SELECT #Net = i.NrUnits * i.UnitNet from inserted i
SELECT #OldNet = d.NrUnits * d.UnitNet from deleted d
IF(#Net=#OldNet)
BEGIN
RETURN
END
SELECT #OrderId = i.OrderId, #JobId = i.JobId, #ItemCode = i.ItemCode FROM inserted i
SELECT #OrderNr = OrderNr, #TaxRate = TaxRate FROM Orders WHERE OrderId = #OrderId
SET #Tax = #Net * #TaxRate / 100
SET #Total = #Net + #Tax
SET #ExactFee = #Total * #syncRate
SET #Fee = FLOOR(#ExactFee * 100)/100
IF(#Fee >= 0.01)
BEGIN
IF #JobId IS NULL
INSERT INTO SubscriptionTransactions
(ItemValue, OrderNr, TransactionCredit, TransactionDate, TransactionDebit, TransactionDescription, TransactionType)
VALUES (#Total, #OrderNr, 0, GetDate(), #Fee, #ItemCode, 'Item')
ELSE
INSERT INTO SubscriptionTransactions
(ItemValue, OrderNr, TransactionCredit, TransactionDate, TransactionDebit, TransactionDescription, TransactionType)
VALUES (#Total, #OrderNr, 0, GetDate(), #Fee, #ItemCode, 'Job')
END
END
However we sometimes get multiple rows in inserted so I included a loop like this
ALTER TRIGGER [dbo].[DebitSale]
ON [dbo].[OrderDetails]
AFTER INSERT, UPDATE
AS
BEGIN
DECLARE #OrderId bigint
DECLARE #OrderDetailId bigint
DECLARE #OrderNr int
DECLARE #TaxRate decimal(9,2)
DECLARE #Tax decimal(9,2)
DECLARE #Total decimal(9,2)
DECLARE #syncRate decimal(9,8)
DECLARE #Net decimal(9,2)
DECLARE #OldNet decimal(9,2)
DECLARE #ExactFee decimal(9,2)
DECLARE #Fee decimal(9,2)
DECLARE #JobId bigint
DECLARE #ItemCode nvarchar(35)
SELECT #syncRate = SyncRate
FROM dbo.[UserAccount]
WHERE Id = 0
DECLARE #current INT = 0;
DECLARE #InsertedCount int
SELECT #InsertedCount = Count(*) FROM inserted
DECLARE #Thing nvarchar(max)
SELECT #Thing ='InsertedCount ' + CAST(#InsertedCount AS VARCHAR)
INSERT INTO DebugTable (DebugColumn) VALUES (#Thing)
WHILE #current <= #InsertedCount
BEGIN
SELECT #Thing ='current ' + CAST(#current AS VARCHAR)
INSERT INTO DebugTable (DebugColumn) VALUES (#Thing)
SELECT #OrderDetailId AS OrderDetailId from inserted i
ORDER BY OrderDetailId
OFFSET #current ROWS
FETCH NEXT 1 ROWS ONLY
SET #current = #current + 1;
SELECT #Net = NrUnits * UnitNet FROM inserted i WHERE i.OrderDetailId= #OrderDetailId
SELECT #OldNet = d.NrUnits * d.UnitNet from deleted d where d.OrderDetailId= #OrderDetailId
IF(#Net=#OldNet)
CONTINUE
SELECT #OrderId = i.OrderId, #JobId = i.JobId, #ItemCode = i.ItemCode FROM inserted i WHERE i.OrderDetailId= #OrderDetailId
SELECT #OrderNr = OrderNr, #TaxRate = TaxRate FROM Orders WHERE OrderId = #OrderId
SET #Tax = #Net * #TaxRate / 100
SET #Total = #Net + #Tax
SET #ExactFee = #Total * #syncRate
SET #Fee = FLOOR(#ExactFee * 100)/100
IF(#Fee < 0.01)
CONTINUE
IF (#JobId IS NULL)
INSERT INTO SubscriptionTransactions
(ItemValue, OrderNr, TransactionCredit, TransactionDate, TransactionDebit, TransactionDescription, TransactionType)
VALUES (#Total, #OrderNr, 0, GetDate(), #Fee, #ItemCode, 'Item')
ELSE
INSERT INTO SubscriptionTransactions
(ItemValue, OrderNr, TransactionCredit, TransactionDate, TransactionDebit, TransactionDescription, TransactionType)
VALUES (#Total, #OrderNr, 0, GetDate(), #Fee, #ItemCode, 'Job')
END
INSERT INTO DebugTable (DebugColumn) VALUES (#ItemCode)
END
This is a remote server that services a Web API. I don't have access to remote debugging so I've put some debug code in that logs a couple of lines to a DebugTable. The trigger writes to DebugTable if I execute an insert statement in SSMS, but doesn't update Transactions.
The Web API executes a merge statement in which case nothing is written to DebugTable and Transactions are not updated. I'm not sure if the new trigger is even firing.
I know there is a lot of TSQL here, but given the original trigger seems to work for a single insert, and that trigger is unchanged except for wrapping it in a loop, I assume I've got the loop wrong.
I expect some will spurn the loop, but in mitigation, there are rarely more than 2 rows inserted at a time.
How do I loop through inserted in a trigger?

Answer 1

Your main insert should be something like the following i.e. there is no need for a loop. One should always aim for set based operations in SQL if at all possible. The key points are:
JOIN the relevant tables together
use CROSS APPLY to avoid having to repeat calculations
use the WHERE clause to exclude cases you are currently using CONTINUE for.
I've tried to match your logic as best I can. But without being able to test it I can't be sure it works. You will want to run it through a few tests to be sure its working exactly as you wish.
And I leave the debugging/logging code as an exercise for you.
INSERT INTO dbo.SubscriptionTransactions (ItemValue, OrderNr, TransactionCredit, TransactionDate, TransactionDebit, TransactionDescription, TransactionType)
SELECT
T.Total
, O.OrderNr
, 0
, GetDate()
, F.Fee
, I.ItemCode
, CASE WHEN I.JobId IS NULL THEN 'Job' ELSE 'Item' END
FROM Inserted I
-- Deleted won't exist for an insert
LEFT JOIN Deleted D on D.OrderDetailId = I.OrderDetailId
INNER JOIN Orders O on O.OrderId = I.OrderId
CROSS APPLY (
VALUES (I.NrUnits * I.UnitNet, D.NrUnits * D.UnitNet)
) N (Net, OldNet)
CROSS APPLY (
VALUES (N.Net * (1.0 + N.Net * O.TaxRate / 100))
) T (Total)
CROSS APPLY (
VALUES (FLOOR(T.Total * #SyncRate * 100)/100)
) F (Fee)
WHERE (N.Net != N.OldNet OR D.OrderDetailId IS NULL) -- First continue condition
AND Fee >= 0.01; -- Second continue condition