Lookup data in one table and update another - sql-server-2008

Question

I need a trigger that fires on update of a particular column in a table, and updates other columns using data from two other tables.
Table 1 is called STOCK_ITEMS
The columns concerned are all foreign keys
Column STOCKGROUP is FK for Table STOCK_GROUPS
Column STOCKGROUP2 is FK for Table STOCK_GROUP2S
Column X_STOCK_GROUP3 is FK for X_STOCK_GROUP3S
Table X_STOCK_GROUP3S contains the FKs of the other two stock group tables.
The idea is to make the first two columns dependent on the third, so that if the value of X_STOCK_GROUP3 changes, this trigger will set the values of STOCKGROUP and STOCKGROUP2 using the data from X_STOCK_GROUP3S
I tried this:
CREATE TRIGGER STOCKGROUP
ON [dbo].[STOCK_ITEMS]
FOR UPDATE
AS
IF UPDATE (X_STOCK_GROUP3)
set STOCKGROUP = STOCK_GROUPS.GROUPNO
PRINT 'AFTER UPDATE Trigger fired.'
GO
It does not work. It does not like my '=' sign. Or is there something else I'm missing (likely!!)
Any and all help appreciated.

Answer 1

Don' know if I understand what you want to do.
X_STOCK_GROUP3S contains some records like
(ID,STOCKGROUP,STOCKGROUP2)
(21,1000,300)
(22,2000,200)
(23,3000,100)
and STOCK_ITEMS contains records like
(ID,...,STOCKGROUP,STOCKGROUP2,X_STOCK_GROUP3)
If X_STOCK_GROUP3 of table STOCK_ITEMS is updated to 21 you want to set the values STOCKGROUP to 1000 and STOCKGROUP2 to 300.
Is this what you want to accomplish?
Then your code is missing some selection criteria.
I would try something like this
CREATE TRIGGER STOCKGROUP
ON [dbo].[STOCK_ITEMS]
FOR UPDATE
AS
SET NOCOUNT ON;
IF UPDATE (X_STOCK_GROUP3)
UPDATE STOCK_ITEMS SET STOCKGROUP = (
SELECT STOCKGROUP FROM X_STOCK_GROUP3S
WHERE STOCK_ITEMS.X_STOCK_GROUP3 = X_STOCK_GROUP3S.ID
),
STOCKGROUP2 = (
SELECT STOCKGROUP2 FROM X_STOCK_GROUP3S
WHERE STOCK_ITEMS.X_STOCK_GROUP3 = X_STOCK_GROUP3S.ID
)
WHERE ID IN (SELECT ID FROM deleted);
GO

Answer 2

OK, so here is the final, and successful, result:
Kudos credit: Sonny Dhaliwal - Support Consultant - Enprise Solutions. Thanks Sonny.
USE [MyDataBase]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TRIGGER [dbo].[X_SET_STOCK_GROUPS]
ON [dbo].[STOCK_ITEMS]
FOR UPDATE
AS
DECLARE #STOCKCODE VARCHAR(100),
#STOCKGROUP3 INTEGER,
#STOCKGROUP1 INTEGER,
#STOCKGROUP2 INTEGER
BEGIN
SELECT #STOCKCODE = STOCKCODE FROM inserted
SELECT #STOCKGROUP3 = X_STOCK_GROUP3 FROM inserted
SELECT #STOCKGROUP1 = (SELECT SECONDARY_GROUP FROM X_STOCK_GROUP3S
WHERE SEQNO = #STOCKGROUP3)
SELECT #STOCKGROUP2 = (SELECT PRIMARY_GROUP FROM X_STOCK_GROUP3S
WHERE SEQNO = #STOCKGROUP3)
BEGIN
UPDATE STOCK_ITEMS
SET STOCKGROUP = #STOCKGROUP1, STOCKGROUP2 = #STOCKGROUP2
WHERE STOCKCODE = #STOCKCODE
END
END
GO