Handling multiple rows in SQL Server trigger - sql-server

Question

We have a database with a table called WarehouseItem where product's stock levels are kept. I need to know when ever this table get's updated, so I created a trigger to put the primary key of this table row that got updated; into a separate table (like a queue system).
This is my trigger:
IF ((SELECT COUNT(*) FROM sys.triggers WHERE name = 'IC_StockUpdate') > 0)
DROP TRIGGER [dbo].[IC_StockUpdate]
GO
CREATE TRIGGER [dbo].[IC_StockUpdate] ON [dbo].[WarehouseItem]
AFTER UPDATE
AS
BEGIN
-- Get Product Id
DECLARE #StockItemID INT = (SELECT ItemID FROM INSERTED);
DECLARE #WarehouseID INT = (SELECT WarehouseID FROM INSERTED);
-- Proceed If This Product Is Syncable
IF (dbo.IC_CanSyncProduct(#StockItemID) = 1)
BEGIN
-- Proceed If This Warehouse Is Syncable
IF (dbo.IC_CanSyncStock(#WarehouseID) = 1)
BEGIN
-- Check If Product Is Synced
IF ((SELECT COUNT(*) FROM IC_ProductCreateQueue WHERE StockItemID = #StockItemID) > 0)
BEGIN
-- Check If Stock Update Queue Entry Already Exists
IF ((SELECT COUNT(*) FROM IC_StockUpdateQueue WHERE StockItemID = #StockItemID) > 0)
BEGIN
-- Reset [StockUpdate] Queue Entry
UPDATE IC_StockUpdateQueue SET Synced = 0
WHERE StockItemID = #StockItemID;
END
ELSE
BEGIN
-- Insert [StockUpdate] Queue Entry
INSERT INTO IC_StockUpdateQueue (StockItemID, Synced) VALUES
(#StockItemID, 0);
END
END
ELSE
BEGIN
-- Insert [ProductCreate] Queue Entry
INSERT INTO IC_ProductCreateQueue (StockItemID, Synced) VALUES
(#StockItemID, 0);
-- Insert [StockUpdate] Queue Entry
INSERT INTO IC_StockUpdateQueue (StockItemID, Synced) VALUES
(#StockItemID, 0);
END
END
END
END
GO
This works perfectly fine, if only a single row is updated in the "WarehouseItem" table.
However, if more than one row is updated in this table, my trigger is failing to handle it:
Is there a way to iterate through the "inserted" collection after a mass update event? Or how does one handle multiple row updates in trigger?

Answer 1

You use this:
-- Get Product Id
DECLARE #StockItemID INT = (SELECT ItemID FROM INSERTED);
DECLARE #WarehouseID INT = (SELECT WarehouseID FROM INSERTED);
But if you update multi rows (as your sample) you must use a different strategy.
For example, instead to declare a variable, use INSERTED table in JOIN in query where now you use your variable.
IF statement works on your variable but I think to move that condition in query.
Try to change you UPDATE query in this way (eventually add condition of IF):
-- Reset [StockUpdate] Queue Entry
UPDATE IC_StockUpdateQueue SET Synced = 0
FROM inserted
WHERE inserted.itemID = StockItemID;
And so on.
For further information please add comment.

Answer 2

You could use a loop to iterate over INSERTED but it may be better to change your scalar variables into a TABLE and INSERT-SELECT from INSERTED where the IDs meet the criteria of the first two IFs
DECLARE #inserted TABLE (StockItemID INT, WarehouseID INT)
INSERT INTO #inserted (StockItemID, WarehouseID)
SELECT StockItemID, WarehouseID
FROM INSERTED i
WHERE dbo.IC_CanSyncProduct(i.StockItemID)=1
AND dbo.IC_CanSyncStock(i.WarehouseID)=1
then you can remove the if else upsert logic and use queries that further filter #inserted for the various updates and inserts that are required
;WITH ResetQueueEntry
(
SELECT StockItemID
FROM #inserted i
WHERE EXISTS(SELECT 1 FROM IC_ProductCreateQueue q WHERE q.StockItemID = i.StockItemID)
AND EXISTS(SELECT 1 FROM IC_StockUpdateQueue q WHERE q.StockItemID = i.StockItemID))
)
-- Reset [StockUpdate] Queue Entry
UPDATE IC_StockUpdateQueue
SET Synced = 0
WHERE StockItemID IN (SELECT StockItemID FROM ResetStockUpdate);
WITH InsertQueueEntry
(
SELECT StockItemId, 0 Synced
FROM #inserted
WHERE EXISTS(SELECT 1 FROM IC_ProductCreateQueue q WHERE q.StockItemID = i.StockItemID)
AND NOT EXISTS(SELECT 1 FROM IC_StockUpdateQueue q WHERE q.StockItemID = i.StockItemID))
)
-- Insert [StockUpdate] Queue Entry
INSERT INTO IC_StockUpdateQueue (StockItemID, Synced)
SELECT StockItemID, Synced
FROM InsertQueueEntry
WITH CreateProductEntry
(
SELECT StockItemId, 0 Synced
FROM #inserted
WHERE NOT EXISTS(SELECT 1 FROM IC_ProductCreateQueue q WHERE q.StockItemID = i.StockItemID)
)
-- Insert [ProductCreate] Queue Entry
INSERT INTO IC_ProductCreateQueue (StockItemID, Synced)
SELECT StockItemId, Synced
FROM CreateProductEntry
WITH CreateStockEntry
(
SELECT StockItemId, 0 Synced
FROM #inserted
WHERE NOT EXISTS(SELECT 1 FROM IC_ProductCreateQueue q WHERE q.StockItemID = i.StockItemID)
)
-- Insert [StockUpdate] Queue Entry
INSERT INTO IC_StockUpdateQueue (StockItemID, Synced)
SELECT StockItemId, Synced
FROM CreateProductEntry

Answer 3

in case of the trigger is for INSERT, UPDATE
this code will exit the trigger IF Records are being updated AND more than one record is being afftected:
IF (SELECT COUNT(*) FROM Deleted) > 1
BEGIN
Return
END
But if you wish to examin every record in the INSERTED recordset you can use this method:
DECLARE rstAST CURSOR FOR
SELECT ins.TaskActionId,
_Task.CustomerId,
_AST.ASTQRId,
ins.ExistingQRcode,
ins.NewQRcode
FROM Inserted ins INNER JOIN
dbo.cdn_AST _AST ON ins.ASTId = _AST.ASTId INNER JOIN
dbo.tsk_Task _Task ON ins.TaskId = _Task.TaskId
OPEN rstAST
FETCH NEXT FROM rstAST INTO #TaskActionId, #TaskCustomerId, #ASTQRId, #ExistingQRcode, #NewQRcode
WHILE ##FETCH_STATUS = 0
BEGIN
--use CONTINUE to skip next record or let it traverse the loop
FETCH NEXT FROM rstAST INTO #TaskActionId, #TaskCustomerId, #ASTQRId, #ExistingQRcode, #NewQRcode
END
CLOSE rstAST
DEALLOCATE rstAST