I have a calculation in my DB need to update "field1" for "table1" after the update trigger.
The problem that updating that field will cause the after update trigger to fire and execute a lengthy procedure and display errors.
please advise how to update the "field1" after the "After update" trigger has been executed and without making the "after update" trigger to execute again.
I know that I can not use NEW with After trigger.
Thanks
One can use a custom locking mechanism based on context variables which prevent from repeating invocation of AFTER UPDATE trigger.
CREATE TRIGGER au FOR table
AFTER UPDATE
POSITION 0
AS
BEGIN
IF RDB$GET_CONTEXT('USER_TRANSACTION', 'MY_LOCK') IS NULL THEN
BEGIN
RDB$SET_CONTEXT('USER_TRANSACTION', 'MY_LOCK', 1);
...
Do your update operations here
...
RDB$SET_CONTEXT('USER_TRANSACTION', 'MY_LOCK', NULL);
END
WHEN ANY DO
BEGIN
RDB$SET_CONTEXT('USER_TRANSACTION', 'MY_LOCK', NULL);
EXCEPTION;
END
END
The obvious answer is to switch to the BEFORE UPDATE trigger, as pointed out by J Cooper... however, if there is some reason you absolutely have to use AFTER UPDATE then you have to set up a flag which tells that the field needs to be recalculated and check it in your trigger. One way to do it would be to set the field to NULL in BEFORE trigger and then check against NULL in AFTER trigger, ie
CREATE TRIGGER bu_trigger BEFORE UPDATE
BEGIN
-- mark field for recalculation if needed
IF(update invalidates the field1 value)THEN
NEW.field1 = NULL;
END
CREATE TRIGGER au_trigger AFTER UPDATE
BEGIN
-- only update if the field is NULL
IF(NEW.field1 IS NULL)THEN
UPDATE table1 SET field1 = ...;
END
But using this technique you probably have to use lot of IF(OLD.field IS DISTINCT FROM NEW.field)THEN checks in triggers to avoid unnessesary updates in your triggers.
simple solution...
fire the update only if the NEW.FIELD1 value is really new, like this:
CREATE TRIGGER au FOR table1
AFTER UPDATE
POSITION 0
AS
DECLARE VARIABLE TMP AS NUMBER(15,5); -- SAME DATATYPE OF FIELD1
BEGIN
-- MAKE YOUR CALCULATION
TMP=CALCULATEDVALUE;
-- UPDATE THE ROW ONLY IF THE VALUES IS CHANGED
IF (TMP<>NEW.FIELD1) UPDATE TABLE1 SET FIELD1=:TMP WHERE KEY=NEW.KEY; -- PAY ATTENTION IF TMP OR NEW.FIELD1 CAN BE NULL. IN THIS CASE USE COALESCE OR A DIFFERENCE COMPARISON
END
Solution: Use BEFORE UPDATE TRIGGER instead of AFTER UPDATE TRIGGER
CREATE TRIGGER some_trigger BEFORE UPDATE ... etc
Related
DROP TRIGGER IF EXISTS N2Trigger
CREATE TRIGGER N2Trigger
ON dbo.Date
FOR INSERT, DELETE
AS
BEGIN
SELECT 'Inserted Datebase' as MESSAGE
SELECT 'Deleted Database' as MESSAGE
END
DELETE FROM dbo.[Date] WHERE ID = 1
Here is my code I just want when I use insert statement return 'Inserted Datebase' as MESSAGE
When I use delete statement return 'Deleted Database' as MESSAGE
The easiest way to check what action fired the trigger is to inspect the inserted and deleted pseudo-tables. If the trigger is only on DELETE/INSERT and not on update, then the logic is simply:
CREATE TRIGGER dbo.trFlarb ON dbo.flarb
FOR INSERT, DELETE
AS
BEGIN
IF EXISTS (SELECT 1 FROM inserted)
BEGIN
SELECT 'Inserted.';
END
IF EXISTS (SELECT 1 FROM deleted)
BEGIN
SELECT 'Deleted.';
END
END
Example db<>fiddle
Now, of course, Marc is right: triggers aren't for returning or printing output. This is just a demonstration that you can use those checks to then perform whatever logic you need to perform in the event of either action.
That said, if you have two distinctly different things you want to do depending on whether it's an insert or a delete, why not just create two separate triggers?
CREATE TRIGGER dbo.tr_I_Flarb ON dbo.flarb
FOR INSERT
AS
BEGIN
SELECT 'Inserted.';
END
GO
CREATE TRIGGER dbo.tr_D_Flarb ON dbo.flarb
FOR DELETE
AS
BEGIN
SELECT 'Deleted.';
END
GO
Note that SELECT will only "work" on your system if you haven't turned on the disallow results from triggers Server Configuration Option. Again, you should try to explain what you really want to do in the event of an insert or update, because the end goal can't be to print or return "Inserted" or "Deleted."
Unable to execute the trigger, Can anyone explain where i am doing wrong.
CREATE OR REPLACE TRIGGER HK_WS_ED_CT_T1
BEFORE INSERT OR UPDATE OF CI On HK_WS_ED_CT
FOR EACH ROW
BEGIN
IF (:new.CI = CI) THEN
UPDATE HK_WS_ED_CT
SET (TRANS_OTHER, TRANS_OTHER_DESC) =
(SELECT TRANS_OTHER, TRANS_OTHER_DESC
FROM HK_WS_ED_CT
where CI = :NEW.CI and rownum <=1 order by DATE)
end if;
END;
You are updating the table the trigger is on. This is not allowed.
You should put :new.trans_other equal to something and :new.trans_other_desc to something.
The update of the field will be ok then.
If you really want to update all the rows of that same table you should take a look at compound triggers. But I doubt this is what you want.
The main problem in DB triggers is you can't select, insert, update, delete from the table the trigger is firing on. The table is locked at this moment.
I'm developing a small library database and I don't want to allow someone to update someone's ID. But I need to use AFTER UPDATE and FOR EACH STATEMENT (which I'm told is Oracle's default). So, basically, if someone updates the customer info and alter his/her ID or mistypes it, the trigger will automatically update it again to the old value. The problem is that Oracle won't let me use :NEW and :OLD when using FOR EACH STATEMENT. Are there any workarounds to this issue?
CREATE OR REPLACE TRIGGER alter_id_trigger
AFTER UPDATE ON CUSTOMER
BEGIN
UPDATE CUSTOMER SET ID = :OLD.ID
WHERE ID = :NEW.ID;
END;
Thank you!
Use the below code for trigger.
Changes done:
Using BEFORE UPDATE instead of AFTER UPDATE.
Setting the value of ID to what it was previously. (The ID Field would never be modified)
CREATE OR REPLACE TRIGGER ALTER_ID_TRIGGER
BEFORE UPDATE ON CUSTOMER
BEGIN
SET :NEW.ID = :OLD.ID
END;
Note: With BEFORE UPDATE:
You can not create a BEFORE trigger on a view.
You can update the :NEW values.
You can not update the :OLD values.
I think you want a before update trigger:
CREATE OR REPLACE TRIGGER alter_id_trigger
BEFORE UPDATE ON CUSTOMER
BEGIN
SET :NEW.ID = :OLD.ID
END;
You could test to see if the value is being changed, but that seems unnecessary.
I have a ruby app. The app is doing the insert,update and delete on a particular table.
It does 2 kinds of INSERT, one insert should insert a record in the table and also into trigger_logs table. Another insert is just to insert the record into the table and do nothing. Another way to put it is, one kind of insert should log that the 'insert' happened into another table and another kind of insert should just be a normal insert. Similarly, there are 2 kinds of UPDATE and DELETE also.
I have achieved the 2 types of INSERT and UPDATE using a trigger_disable. Please refer to the trigger code below.
So, when I do a INSERT, I will set the trigger_disable boolean to true if I don't want to log the trigger. Similarly I am doing for an UPDATE too.
But I am not able to differentiate between the 2 kinds of DELETE as I do for an INSERT or UPDATE. The DELETE action is logged for both kinds of DELETE.
NOTE: I am logging all the changes that are made under a certain condition, which will be determined by the ruby app. If the condition is not satisfied, I just need to do a normal INSERT, UPDATE or DELETE accordingly.
CREATE OR REPLACE FUNCTION notify_#{#table_name}()
RETURNS TRIGGER
LANGUAGE plpgsql
AS $$
DECLARE
changed_row_id varchar(100);
BEGIN
IF TG_OP = 'DELETE' THEN
-- When the trigger is due to a delete
IF (OLD.trigger_disable IS NULL)
OR (OLD.trigger_disable = false) THEN
-- Prevent the trigger if trigger_disable is 'true'
-- The Problem is here: This insertion into the
-- trigger_logs table happens
-- for all the delete statements.
-- But during certain deletes I should not
-- insert into trigger_logs
INSERT INTO trigger_logs (table_name, action, row_id, dirty)
VALUES (
'#{#table_name}',
CAST(TG_OP AS Text),
OLD.id,
true
) RETURNING id into changed_row_id;
END IF;
RETURN OLD;
ELSE
-- The trigger is due to a Insert or Update
IF (NEW.trigger_disable IS NULL)
OR (NEW.trigger_disable = false) THEN
-- Prevent the trigger if trigger_disable is 'true'
INSERT INTO trigger_logs (table_name, action, row_id, dirty)
VALUES (
'#{#table_name}',
CAST(TG_OP AS Text),
NEW.id,
true
) RETURNING id into changed_row_id;
ELSE
NEW.trigger_disable := false;
END IF;
RETURN NEW;
END IF;
END
I'm going to take a stab in the dark here and guess that you're trying to contextually control whether triggers get fired.
If so, perhaps you can use a session variable?
BEGIN;
SET LOCAL myapp.fire_trigger = 'false';
DELETE FROM ...;
COMMIT;
and in your trigger, test it:
IF current_setting('myapp.fire_trigger') = 'true' THEN
Note, however, that if the setting is missing from a session you won't get NULL, you'll get an error:
regress=> SELECT current_setting('myapp.xx');
ERROR: unrecognized configuration parameter "myapp.xx"
so you'll want to:
ALTER DATABASE mydb SET myapp.fire_trigger = 'true';
Also note that the parameter is text not boolean.
Finally, there's no security on session variables. So it's not useful for security audit, since anybody can come along and just SET myapp.fire_trigger = 'false'.
(If this doesn't meet your needs, you might want to re-think whether you should be doing this with triggers at all, rather than at the application level).
I have table A and there is a column name COL_A.
I want that if someone change the value, lets say from 1 to 'X' (not costant) that the trigger will change it back from 'X' to 1.
SQLite does not support changing the new column values.
The only way to change a column in a trigger would be to run an UPDATE command,
but that would run the trigger again.
What you can do is to prevent changing the column in the first place:
CREATE TRIGGER IF NOT EXISTS prevent_col_a_change
BEFORE UPDATE OF col_a ON a
BEGIN
SELECT RAISE(ABORT, 'COL_A must not be changed');
END;
UPDATE trigger is a good solution for your case. Just set old value to the new value, that will lead to behaviour you want.
For example:
CREATE OR REPLACE TRIGGER orders_before_update
BEFORE UPDATE
ON orders
FOR EACH ROW
BEGIN
:new.CreatedAt:= :old.CreatedAt;
END;