After Update Trigger puzzlement - sql

Question

I am trying to get my head round an AFTER UPDATE trigger.
Currently in our DB there is a Trigger that contains a cursor. From my understanding cursors in triggers are generally bad performing, so I'm trying to get rid of the cursor.
Currently the trigger looks like this:
ALTER TRIGGER [dbo].[trg_TaskMovement_Zone] ON [dbo].[Tasks_Movement]
AFTER INSERT, UPDATE
AS
BEGIN
SET NOCOUNT ON
DECLARE #rowcheck int
DECLARE #MovementID INT
DECLARE #SiteFromID INT
DECLARE #SiteToID INT
DECLARE #SiteResponsibleID INT
DECLARE #FromAddress_Postcode Varchar(20)
DECLARE #ToAddress_Postcode Varchar(20)
DECLARE zcursor CURSOR FOR SELECT ID, SiteFromID, SiteToID, SiteResponsibleID
, FromAddress_Postcode, ToAddress_Postcode FROM inserted
OPEN zcursor
SELECT #rowcheck=1
WHILE #rowcheck=1
BEGIN
FETCH NEXT FROM zcursor INTO #MovementID, #SiteFromID, #SiteToID, #SiteResponsibleID, #FromAddress_Postcode, #ToAddress_Postcode
IF (##FETCH_STATUS = 0)
BEGIN
UPDATE Tasks_Movement
SET ZoneFromID = dbo.fn_GetZoneFromPostcode(#FromAddress_Postcode),
ZoneToID = dbo.fn_GetZoneFromPostcode(#ToAddress_Postcode)
WHERE Tasks_Movement.ID = #MovementID
UPDATE Tasks_Movement
SET SiteResponsibleID = [dbo].[fn_GetDefaultDepotResponsibleForSite](#SiteFromID)
WHERE Tasks_Movement.ID = #MovementID
AND (#SiteResponsibleID Is NULL OR #SiteResponsibleID=0)
AND (#SiteFromID Is NOT NULL AND #SiteFromID>0)
UPDATE Tasks_Movement
SET SiteResponsibleID = [dbo].[fn_GetDefaultDepotResponsibleForSite](#SiteToID)
WHERE Tasks_Movement.ID = #MovementID
AND (#SiteResponsibleID Is NULL OR #SiteResponsibleID=0)
AND (#SiteToID Is NOT NULL AND #SiteToID>0)
END
ELSE
SELECT #rowcheck=0
END
CLOSE zcursor
DEALLOCATE zcursor
END
From what I can tell the cursor in this is completely unnecessary(?)
Would I be right in thinking that the following would work better:
ALTER TRIGGER [dbo].[trg_TaskMovement_Zone] ON [dbo].[Tasks_Movement]
AFTER INSERT, UPDATE
AS
BEGIN
SET NOCOUNT ON
UPDATE Tasks_Movement
SET ZoneFromID = dbo.fn_GetZoneFromPostcode(inserted.FromAddress_Postcode),
ZoneToID = dbo.fn_GetZoneFromPostcode(inserted.ToAddress_Postcode)
FROM inserted
WHERE Tasks_Movement.ID IN (SELECT id FROM inserted)
UPDATE Tasks_Movement
SET SiteResponsibleID = [dbo].[fn_GetDefaultDepotResponsibleForSite](inserted.SiteFromID)
FROM inserted
WHERE Tasks_Movement.ID IN (SELECT id FROM inserted
WHERE (inserted.SiteResponsibleID Is NULL OR inserted.SiteResponsibleID=0)
AND (inserted.SiteFromID Is NOT NULL AND inserted.SiteFromID>0))
UPDATE Tasks_Movement
SET SiteResponsibleID = [dbo].[fn_GetDefaultDepotResponsibleForSite](#SiteToID)
FROM inserted
WHERE Tasks_Movement.ID IN (SELECT id FROM inserted
WHERE (inserted.SiteResponsibleID Is NULL OR inserted.SiteResponsibleID=0)
AND (inserted.SiteToID Is NOT NULL AND inserted.SiteToID>0))
END

Answer 1

I think your trigger should be something like this:
ALTER TRIGGER [dbo].[trg_TaskMovement_Zone] ON [dbo].[Tasks_Movement]
AFTER INSERT, UPDATE
AS
BEGIN
SET NOCOUNT ON
UPDATE tm
SET ZoneFromID = dbo.fn_GetZoneFromPostcode(i.FromAddress_Postcode),
ZoneToID = dbo.fn_GetZoneFromPostcode(i.ToAddress_Postcode)
FROM Tasks_Movement tm
INNER JOIN inserted i
ON i.ID = tm.ID;
UPDATE tm
SET SiteResponsibleID = [dbo].[fn_GetDefaultDepotResponsibleForSite](i.SiteFromID)
FROM Tasks_Movement tm
INNER JOIN inserted i
ON i.ID = tm.ID
WHERE (i.SiteResponsibleID IS NULL OR i.SiteResponsibleID = 0)
AND i.SiteFromID > 0
UPDATE tm
SET SiteResponsibleID = [dbo].[fn_GetDefaultDepotResponsibleForSite](i.SiteToID)
FROM Tasks_Movement tm
INNER JOIN inserted i
ON i.ID = tm.ID
WHERE (i.SiteResponsibleID IS NULL OR i.SiteResponsibleID = 0)
AND i.SiteToID > 0
END
I've changed it to use SQl Server's UPDATE .. FROM syntax, and also removed the redundant null check when you are checking if a site ID > 0. NULL is not greater than or less than 0, so if SiteID is null SiteID > 0 can never evaluate to true, so it is a redundant additional check.
Finally, I would also recommend removing the user defined functions, although I can't see under the hood of these, based on the name they look very much like they are simple loukup functions that could be achived much more efficiently with joins.
EDIT
Rather than using the UPDATE(column) function I would add an additional join to the update to filter for updated rows, e.g.:
UPDATE tm
SET SiteResponsibleID = [dbo].[fn_GetDefaultDepotResponsibleForSite](i.SiteToID)
FROM Tasks_Movement tm
INNER JOIN inserted i
ON i.ID = tm.ID
LEFT JOIN deleted d
ON d.ID = i.ID
WHERE (i.SiteResponsibleID IS NULL OR i.SiteResponsibleID = 0)
AND i.SiteToID > 0
AND AND ISNULL(i.SiteToID, 0) != ISNULL(d.SiteToID);
I'd do it this way because UPDATE(siteToID) will return true if any row has an updated value, so if you update 1,000,000 rows and one has a change it will perform the update on all of them, not just the ones that have changed, by joining to deleted you can limit the update to relevant rows.