issue with trigger in ms sql server? - sql

Question

IF EXISTS (SELECT name FROM sysobjects WHERE name = 'myTrigger' AND type = 'TR')
BEGIN
DROP TRIGGER myTrigger
END
GO
go
create trigger myTrigger
on mytable_backup
instead of insert
as
begin
declare #seq int
select #seq = seq from inserted
if exists (select * from mytable_backup where seq= #seq) begin
delete from mytable_backup where seq=#seq
end
insert into mytable_backup
select * from inserted
end
go
I've written this trigger to check while inserting if seq column is repeated then update the previous row with same seq if seq doesn't exits insert it with new seq.
In ssis package I'm using OLEDB table(Mytable) as a source which contains.
Name,Age,Seq
Gauraw,30,1
Gauraw,31,1
Kiran,28,3
Kiran,29,3
kiran,28,3
Venkatesh,,4
Venkatesh,28,4
Now I'm loading this table to OLEDB destination(Mytable_backup) as destination.
I suppose to get output as.
Gauraw,31,1
kiran,28,3
Venkatesh,28,4
But I'm getting all the records from Mytable into Mytable_backup.
is anything wrong with my trigger?

Answer 1

I think that this trigger will just take the first row and compare it with the existing. If I understand what you want to do you can quit easy do this:
IF EXISTS (SELECT name FROM sysobjects WHERE name = 'myTrigger' AND type = 'TR')
BEGIN
DROP TRIGGER myTrigger
END
GO
go
create trigger myTrigger
on mytable_backup
instead of insert
as
begin
insert into mytable_backup
select
*
from
inserted
WHERE NOT EXISTS
(
SELECT
NULL
FROM
mytable_backup AS mytable
WHERE
inserted.seq=mytable.seq
)
end
go
EDIT
So I found out what was going on. If you insert all of the rows in one go the inserted contains all the rows.. Sorry my mistake. If there are duplicates in your data your example do not show which to choose. I have chosen the one with the maximum of age (don't know what your requirements is). Here is a update with the full example
Table structure
CREATE TABLE mytable_backup
(
Name VARCHAR(100),
Age INT,
Seq INT
)
GO
Trigger
create trigger myTrigger
on mytable_backup
instead of insert
as
begin
;WITH CTE
AS
(
SELECT
ROW_NUMBER() OVER(PARTITION BY inserted.Seq ORDER BY Age) AS RowNbr,
inserted.*
FROM
inserted
WHERE NOT EXISTS
(
SELECT
NULL
FROM
mytable_backup
WHERE
mytable_backup.Seq=inserted.Seq
)
)
insert into mytable_backup(Age,Name,Seq)
SELECT
CTE.Age,
CTE.Name,
cte.Seq
FROM
CTE
WHERE
CTE.RowNbr=1
end
GO
Insert of test data
INSERT INTO mytable_backup
VALUES
('Gauraw',30,1),
('Gauraw',31,1),
('Kiran',28,3),
('Kiran',29,3),
('kiran',28,3),
('Venkatesh',20,4),
('Venkatesh',28,4)
SELECT * FROM mytable_backup
Drop of the database objects
DROP TRIGGER myTrigger
DROP TABLE mytable_backup

Answer 2

Your original code has two flaws:
It assumes that only one record is inserted at a time.
Your insert into mytable_backup happens outside of the if condition. That insert will execute every time.