Procedure which modify existing trigger - sql

Question

I want to create procedure which modify existing trigger. Trigger is responsible for blocking rows from beeing updated with specific ID. I tried something like that:
CREATE PROCEDURE Change_trigger
#List_of_ids varchar(8000)
AS
ALTER TRIGGER blocks
ON ttt
INSTEAD OF update
AS
BEGIN
If (SELECT Id_ttt FROM inserted) IN (#List_of_ids)
BEGIN
raiserror('You cannot modify this record.', 12, 1)
RETURN
END
UPDATE ttt
SET
field1 = INSERTED.field1
FROM INSERTED
WHERE INSERTED.Id_ttt = ttt.Id_ttt
END
Parameter #List_of_ids would be like this: 2,3,4,5,9,52. But when I try to create this procedure I got error:
Msg 156, Level 15, State 1, Procedure Change_trigger, Line 4
Incorrect syntax near the keyword 'TRIGGER'.
The trigger is created.

Answer 1

This is the trigger I'd write, once.
ALTER TRIGGER blocks
ON ttt
INSTEAD OF update
AS
BEGIN
SET NOCOUNT ON
UPDATE t
SET
field1 = i.field1
FROM INSERTED i
inner join
ttt t
on i.Id_ttt = t.Id_ttt
left join
ttt_blocked on tb
on
i.Id_ttt = tb.Id_ttt
WHERE
tb.Id_ttt is null
END
Note that this trigger no longer throws an error for blocked updates but it does allow for a mixed update (some rows blocked, some rows not) to occur. There's no clean way to raise an error whilst still partially applying an update in a trigger.
Then I'd have a table (referenced above):
CREATE TABLE ttt_blocked (
Id_ttt int not null,
constraint PK_ttt_blocked PRIMARY KEY (Id_ttt)
)
And then, if necessary, I'd create a procedure to maintain this table rather than continually changing the database schema:
CREATE PROCEDURE Change_blocking
#BlockedIDs xml
AS
--Better option would be table-valued parameters
--but I've chosen to do XML today
--We expect the XML to be of the form
--<blocks>
-- <id>10</id>
-- <id>15</id>
--</blocks>
MERGE INTO ttt_blocked t
USING (select x.id.value('text()[1]','int')
from #BlockedIDs.nodes('/blocks/id') x(id)) s(Id_ttt)
ON
t.Id_ttt = s.Id_ttt
WHEN NOT MATCHED THEN INSERT (Id_ttt) VALUES (s.Id_ttt)
WHEN NOT MATCHED BY SOURCE THEN DELETE;
As I also allude to above, I'd generally recommend Table-Valued Parameters rather than XML (and either of them ahead of varchar since they're designed to hold multiple values) but it would have added even more code to this answer.

Answer 2

Try this..
CREATE PROCEDURE Change_trigger
#List_of_ids varchar(4000)
AS
begin
declare #sql varchar(8000)
set #sql ='
ALTER TRIGGER blocks
ON ttt
INSTEAD OF update
AS
BEGIN
if exists (SELECT Id_ttt FROM inserted where Id_ttt IN ('+#List_of_ids+'))
BEGIN
raiserror(''You cannot modify this record.'', 12, 1)
RETURN
END
UPDATE ttt
SET
field1 = INSERTED.field1
FROM INSERTED
WHERE INSERTED.Id_ttt = ttt.Id_ttt
END' ;
exec (#sql);
END