SQL Trigger after insert update - sql-server

Question

What is wrong with this code.
If i type like this
Declare tmp as CURSOR FOR
Select i.ID from Inserted
OPEN tmp
Or if i type
Declare tmp as CURSOR FOR
Select i.ID from Deleted
OPEN tmp
Works like a charm but
Is there any way i can write something like this
if #operation <> 3
set #tmp = 'SELECT i.id FROM inserted i '
else
set #tmp =' SELECT i.id FROM deleted i '
DECLARE tmpUpit CURSOR FOR
#tmp
OPEN tmpUpit
Edit :
CREATE TRIGGER [dbo].[ax_Triger] ON [dbo].[extraTable]
FOR INSERT, UPDATE, DELETE AS
SET NOCOUNT ON;
--Capture the Operation (Inserted, Deleted Or Updated)
DECLARE #operation int
DECLARE #Count AS INT
SET #operation = 1
SELECT #Count = COUNT(*)
FROM DELETED
IF #Count > 0
BEGIN
SET #operation = 3
SELECT #Count = COUNT(*)
FROM INSERTED
IF #Count > 0
SET #operation = 2
END
DECLARE tmpUpit CURSOR FOR
SELECT i.id FROM inserted i
OPEN tmpUpit
FETCH NEXT FROM tmpUpit
into #ID WHILE ##fetch_status = 0
begin If Not exists
(SELECT * FROM mytable
where (Operation=3 OR (Operation=1 AND ID=#ID)) AND Status = 0 AND Tablename ='extraTable')
begin INSERT INTO
mytable ([Field1], [Field2],
[ID], [Tablename], [Operation], [Time12], [Status])
VALUES (#Field1, #Field2, #ID, 'extraTable', #operation,GETDATE(),0)
DELETE FROM mytable
WHERE [Field1]=#Field1 And [Field2]=#Field2 And [ID]=#ID And [Tablename]='extraTable'
AND [Operation] = 4 AND [Status] = 0
End
FETCH NEXT FROM tmpUpit into #ID
End CLOSE tmpUpit DEALLOCATE tmpUpit end
i need to insert the value from one table to another depending about the status Inserted/updated/deleted

Answer 1

This is completely untested since the table structures posted did not match the posted trigger code. This should at least demonstrate how you can rethink about this as set based logic instead of row by agonizing row.
CREATE TRIGGER [dbo].[Trigger212] ON [dbo].[Towns]
FOR INSERT, UPDATE, DELETE AS
BEGIN
SET NOCOUNT ON;
DECLARE #operation int
DECLARE #Variable1 nvarchar(8) = 'Woof'
DECLARE #Variable2 nvarchar(4) = 'Foof'
--Capture the Operation (Inserted, Deleted Or Updated)
IF EXISTS(SELECT * FROM inserted) AND NOT EXISTS (SELECT * FROM deleted)
SET #operation = 1 --Insert
ELSE
IF EXISTS(SELECT * FROM inserted) AND EXISTS (SELECT * FROM deleted)
SET #operation = 2 --update
ELSE
SET #operation = 3 -- DELETE
INSERT Requests
(
Field1
, Field2
, ID
, TableName
, Operation
, TimeU
, Status
)
SELECT 'Woof'
, 'Foof'
, i.ID
, 'Towns'
, #operation
, GETDATE()
, 0
FROM inserted i
LEFT JOIN Requests r on r.ID = i.ID
AND r.Operation = 3
OR (r.Operation = 1 and r.ID = i.ID)
AND r.Status = 0
AND r.TableName = 'Towns'
WHERE r.ID IS NULL
DELETE r
FROM Requests r
JOIN inserted i on i.Field1 = r.Field1
AND i.Field2 = r.Field2
AND i.ID = r.ID
AND i.Operation <> #operation
WHERE r.TableName = 'Towns'
AND r.Status = 0
END
In general I think triggers should be avoided but they have their place. When triggers are appropriate I am generally not a big fan of doing all three operations. Over time it gets really messy because invariably you need to do different logic for the different operations. Splitting them into three triggers makes this eventuality a lot less painful for maintenance.