Question

I’ve got problems with my triggers (add and delete):

ALTER TRIGGER [trgAfterShoppingInserted]
ON [ShopingList] AFTER INSERT 
AS BEGIN
   DECLARE @cardId char(6), @points int, @userId int

   SET @cardId = (SELECT cardId FROM inserted)
   SET @points = (SELECT points FROM inserted)
   SET @userId = (SELECT userId from [Card] WHERE id = @cardId)
   IF @userId = 0
   BEGIN
   Update [Card]
   set points = points + @points
   where id =@cardId
   END
   ELSE
   Update [Card]
   set points = points + @points
   where id =@cardId OR
   userId = @userId
END


ALTER TRIGGER [trgAfterShoppingDeleted]
ON [ShopingList] AFTER DELETE 
AS BEGIN
   DECLARE @cardId char(6), @points int, @userId int

   SET @cardId = (SELECT cardId FROM inserted)
   SET @points = (SELECT points FROM inserted)
   SET @userId = (SELECT userId from [Card] WHERE id = @cardId)
   IF @userId = 0
   BEGIN
   Update [Card]
   set points = points - @points
   where id =@cardId
   END
   ELSE
   Update [Card]
   set points = points - @points
   where id =@cardId OR
   userId = @userId
END

The problem is on the SET @cardId..

The error is:

Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.

how is it possibile ?

thanks for any help

Answer 1

Both triggers will not work if your insert or delete statement should ever insert or delete multiple rows. You need to stop assuming that your trigger only deals with a single row – that’s just not the case. You need to rewrite your triggers to handle multiple rows at once (in the Inserted and Deleted tables)

As an example – you could rewrite your trgAfterShoppingDeleted something like this:

ALTER TRIGGER [trgAfterShoppingDeleted]
ON [ShopingList] AFTER DELETE 
AS BEGIN
   UPDATE [Card]
   SET points = points - i.points
   FROM Inserted i
   WHERE Card.id = i.id AND i.UserId = 0

   UPDATE [Card]
   SET points = points - @points
   FROM Inserted i
   WHERE i.UserId <> 0 AND (Card.id = i.id OR Card.userId = i.userId)
END

You need to think in sets of data – don’t assume single rows in your trigger pseudo tables, and don’t do RBAR (row-by-agonizing-row) processing in a trigger.