SQL Trigger & Inserted Idenities - sql

Question

I've got a problem with a trigger that i can't figure out.
Assume i have two tables, Stu_Table2 & Stu_log. Stu_table2 has some columns, one of which is an automatically generated primary key [stu_id]. The link between the two tables is [stu_name]=[user_id]
The below code works fine for Updates & Deletions (as the primary key already exists). But i'm stuck on the insert - how can i insert the automatically generated primary key from stu_name to log table if it hasn't been generated yet?
Stu_name columns, [stu_id] [Stu_name] [Stu_class]
Stu_log columns, [user_id] [stu_name]
obviously this isn't a real world example, just testing proof of concept.
ALTER TRIGGER [dbo].[stu_testtrigger]
ON [dbo].[Stu_Table2] FOR INSERT, UPDATE, DELETE
AS
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with caller queries SELECT statements.
-- If an update/insert/delete occurs on the main table, the number of records affected
-- should only be based on that table and not what records the triggers may/may not
-- select.
SET NOCOUNT ON;
--
-- Variables Needed for this Trigger
--
DECLARE #stu_ID int
DECLARE #stu_name varchar(15)
DECLARE #stu_class int
--
-- Determine if this is an INSERT,UPDATE, or DELETE Action
--
DECLARE #Action as char(1)
DECLARE #Count as int
SET #Action = 'I' -- Set Action to 'I'nsert by default.
SELECT #Count = COUNT(*) FROM DELETED
if #Count > 0
BEGIN
SET #Action = 'D' -- Set Action to 'D'eleted.
SELECT #Count = COUNT(*) FROM INSERTED
IF #Count > 0
SET #Action = 'U' -- Set Action to 'U'pdated.
END
if #Action = 'D'
-- This is a DELETE Record Action
--
BEGIN
SELECT #Stu_id =[stu_id]
,#Stu_name = [stu_name]
FROM DELETED
DELETE [dbo].[stu_log]
WHERE [user_id]=#stu_id
END
Else
BEGIN
--
-- Table INSERTED is common to both the INSERT, UPDATE trigger
--
SELECT #stu_id =[stu_id]
,#stu_name = [stu_name]
FROM INSERTED
if #Action = 'I'
-- This is an Insert Record Action
--
--THIS IS WHERE I'm STUCK i think!!!
BEGIN
INSERT INTO [stu_log]
([user_id]
,[description])
VALUES
(#stu_id
,#stu_name)
END
else
-- This is an Update Record Action
--
BEGIN
UPDATE [stu_log]
SET [user_id] = #stu_id
,[description] = #Stu_name
WHERE [user_id]=#stu_id
END
END
HELP!

Answer 1

Since you seem to want to carry out distinctly different actions for inserts, updates and deletes, I'm not sure why you're cramming all of the actions into a single trigger. I'd just have:
CREATE TRIGGER [dbo].[stu_testtrigger_I]
ON [dbo].[Stu_Table2] AFTER INSERT
AS
INSERT INTO stu_log ([user_id],[description])
SELECT stu_id,stu_name from inserted
GO
CREATE TRIGGER [dbo].[stu_testtrigger_D]
ON [dbo].[Stu_Table2] AFTER DELETE
AS
DELETE FROM stu_log WHERE [user_id] IN (
SELECT stu_id from deleted)
GO
CREATE TRIGGER [dbo].[stu_testtrigger_U]
ON [dbo].[Stu_Table2] AFTER UPDATE
AS
UPDATE l SET user_name = i.user_name
FROM
stu_log l
inner join
inserted i
on l.[user_id] = i.stu_id
GO
Notes:
This works for multi-row inserts, updates and deletes, which your original didn't
I've said AFTER instead of FOR, to make it clearer to you that these actions occur after any activity in Stu_Table2 has already occurred (e.g. the identity value has already been generated, which seems to be your concern).
You should note, however, that AFTER and FOR are synonymous. You'd only get different behaviour if we were doing an INSTEAD OF trigger.
I removed the pointless [user_id] = #stu_id setting from the UPDATE. Given the WHERE clause of this update (or my join equivalent, above), those two must already be equal.