Want to create a trigger where I have two table "A" and "B" and table "A" has already some records in it so i want to write a trigger in table "B" where i want to check condition if table "A" has already the record exist which is inserting then do not insert or fire a trigger of table "B" if record is not exist in table "A" then fire a trigger and insert a record into the table.
As SQL Server doesn't have BEFORE INSERT triggers to alter that insertion before its done, I would use an INSTEAD OF INSERT trigger (your trigger code is executed instead of the usual insertion, so you can add your checks and/or additional actions).
This trigger sample will only insert rows in A when they don't exist in B:
CREATE TRIGGER tr_a_ioi ON A
INSTEAD OF INSERT
AS BEGIN
insert into A
select I.*
from inserted I
left join B on B.PK_Field = I.PK_Field
where B.PK_Field is null -- no corresponding row is found in B
END
You can write similar INSTEAD OF UPDATE and INSTEAD OF DELETE triggers to do additional checks or actions when trying to update or delete rows in A.
Related
Need help in writting a Trigger to update a record to NULL whenever there is an insert or update on a row in the table in Oracle DB.
CODE
create or replace trigger updateRowToNull
AFTER
UPDATE OR INSERT
ON CUSTOMER for each row
BEGIN
update customer set customeraddr=NULL;
END;
A trigger cannot modify the table to which it is attached with a separate transaction. A "before" trigger can, however, manipulate column values within the transaction that causes it to be fired.
create or replace trigger update_row_to_null
before update or insert on customer
for each row
begin
:new.customeraddr := null;
end;
I have two exactly same tables. My question: is there any way when i'm inserting something in first table automatically sql server to copy this row into another table.
I know that i can do it manually
select * into table1 from table2 where table2ID=#table2ID
But i'm wondering if i can create a table dynamically and set it when a row is inserted, copy row's data into another table also.
So with this way i dont need to run extra code to do that, sql will do this automatically
You can use a TRIGGER which is an object that you link to a table with a particular operation (INSERT, UPDATE, DELETE or any combination of those). The trigger's code will execute on each operation done to the linked table.
Basic example:
CREATE TRIGGER dbo.CopyToTable2 ON Table1
AFTER INSERT -- The trigger will execute after any insert done to Table1
AS
BEGIN
SET NOCOUNT ON
INSERT INTO Table2 (
Column1,
-- OtherColumns
)
SELECT
I.Column1
-- OtherColumns
FROM
inserted AS I -- "inserted" is a special table that references the trigger's tracking table for new or updated records
END
The use of a trigger is appropriate here. It might look something like this:
CREATE TRIGGER SomeTriggerName ON theSourceTable
FOR INSERT
AS
INSERT INTO DestinationTable
(column1, someothercolumn)
SELECT (column1, someothercolumn)
FROM inserted
Lets say we have three tables in MSSQL database, A, B and C.
I have a trigger on A after update. This trigger takes some values from B and inserts them into C.
The transaction performs operations in following order:
Begin transaction.
Insert a record into table B.
Update previously inserted (in step 2) record in table B.
Update table A (trigger is triggered).
Trigger inserts into table C some values from inserted in step 2 row.
End of transaction.
The problem is, that values inserted into table C based on the row in table B are only the values from right after the B record was inserted, and do not contain the changes made during the updated operation.
Why?
Trigger code:
CREATE TRIGGER MYTRIGGER ON [dbo].[A] AFTER INSERT, UPDATE AS
BEGIN
INSERT INTO C (SOME_TEXT_VALUE) SELECT SOME_TEXT_VALUE FROM B;
END
GO
Am facing a problem with trigger.
I created a trigger for a table like this
ALTER TRIGGER [dbo].[manageAttributes]
ON [dbo].[tr_levels]
AFTER insert
AS
BEGIN
set nocount on
declare #levelid int
select #levelid=levelid from inserted
insert into testtable(testid) values(#levelid)
-- Insert statements for trigger here
END
But when I insert rows into table tr_levels like this
insert int tr_levels (column1,colum2) values(1,2)
trigger triggered perfectly
But when I tried to insert into table as a bulk like this
insert int tr_levels (column1,colum2) values(1,2),(3,4),(5,6)..
Trigger doesnt fires for all the rows. It fires only one time for the first row. Is that bug with SQL or is there a solution to trigger the trigger for all rows insertion in a bulk insert query
No, it does fire for all rows - once - but you're ignoring the other rows by acting as if inserted only contains one. select #scalar_variable=column from inserted will arbitrarily retrieve a value from one of the rows and ignore the others. Write a set-based insert using inserted in a FROM clause
You need to treat inserted as a table that can contain 0, 1 or multiple rows. So, something like:
ALTER TRIGGER [dbo].[manageAttributes]
ON [dbo].[tr_levels]
AFTER insert
AS
BEGIN
set nocount on
insert into testtable(testid)
select levelid from inserted
END
You have the same issue many people have that: you think the trigger is fired per row. It is not - it is per operation. And inserted is a table. You take one (random) value and ignore the rest. Fix that and it will work.
Triggers fire once per statement in the base table. So if you insert 5 rows in one statement, the trigger fires once and inserted has the 5 rows.
I don't write T-SQL code too often so how do I capture updated row in a trigger?
If I create a trigger for INSERT I can ask for records from inserted as in
Create Trigger [dbo].[tr_test]
on table1
for INSERT
as
declare #id int
select #id = i.RecordId from inserted as I
...
How do I do that for UPDATE?
There are are two trigger or magic tables in sql server that is inserted or deleted table.
If you are creating trigger for Insert
- data comes in only inserted table in deleted table there is no records find
Create Trigger [dbo].[tr_test]
on table1
for INSERT
as
if exists (select 1 from inserted) and not exists(select 1 from deleted)
-- Action which would you want For Insert
If you are creating trigger for Update
- updated data comes in only inserted table and previous data comes in deleted table there is no records find
Create Trigger [dbo].[tr_test]
on table1
for UPDATE
as
if exists (select 1 from inserted) and exists(select 1 from deleted)
-- Action which would you want when your target table has been update
If you are creating trigger for Delete
- Deleted data comes in Deleted table and in case of deleting data it not comes inserted table.
Create Trigger [dbo].[tr_test]
on table1
after Delete
as
if exists (select 1 from deleted ) and not exists(select 1 from inserted)
-- Action which would you want when your target table has been delete
The same way as with an insert trigger. In an update trigger, inserted contains the new values, and deleted contains the old.
Quoth the docs:
The deleted table stores copies of the affected rows during DELETE and UPDATE statements. During the execution of a DELETE or UPDATE statement, rows are deleted from the trigger table and transferred to the deleted table. The deleted table and the trigger table ordinarily have no rows in common.
The inserted table stores copies of the affected rows during INSERT and UPDATE statements. During an insert or update transaction, new rows are added to both the inserted table and the trigger table. The rows in the inserted table are copies of the new rows in the trigger table.
An update transaction is similar to a delete operation followed by an insert operation; the old rows are copied to the deleted table first, and then the new rows are copied to the trigger table and to the inserted table.
Source: DML Triggers, Use the inserted and deleted Tables