I need to clean up a deleted object within another object which uses it as a foreign key, and I use a BEFORE DELETE trigger for that. I have no idea why the code below does not work.
Even more strange is that if I perform sequentially the UPDATE query and then DELETE query, the row is deleted properly.
CREATE OR REPLACE FUNCTION cleanNoteEventConnections() RETURNS TRIGGER AS $$
DECLARE
BEGIN
EXECUTE 'update invoice set "noteEvent"=null where "noteEvent"=' || OLD.id;
RETURN NULL;
END;
$$ LANGUAGE 'plpgsql';
CREATE TRIGGER cleanNoteEventConnections BEFORE DELETE ON note_event
FOR EACH ROW EXECUTE PROCEDURE cleanNoteEventConnections();
This is what I see in the pgAdmin console after the delete query:
delete from note_event where id=34
result: Query returned successfully: 0 rows affected, 11 msec execution time.
And the note_event with id 34 still exists.
This behavior is described in the documentation:
Row-level triggers fired BEFORE can return null to signal the trigger manager to skip the rest of the operation for this row (i.e., subsequent triggers are not fired, and the INSERT/UPDATE/DELETE does not occur for this row). If a nonnull value is returned then the operation proceeds with that row value.
Use RETURN OLD; instead of RETURN NULL;.
Related
Is there any variant to create a trigger before insert and if the value is a value that exists already in table, just update it. I know about 'ON DUBLICATE KEY' or a 'ON CONFLICT' in PostgreSQL but I need a trigger just because it's a task in my university.
I tried to create it, but I get just an error about duplicate keys.
CREATE or replace FUNCTION trigger_function()
RETURNS TRIGGER
LANGUAGE PLPGSQL
AS $$
BEGIN
IF new.name in (select name from "Test")
then
update "Test" set intt = new.intt where name = new.name;
end if ;
return new;
END;
$$
CREATE TRIGGER trigger_name
BEFORE insert
ON "Test"
for each row
EXECUTE PROCEDURE trigger_function();
Is it possible to create such trigger?
Read the docs plpgsql trigger function:
Row-level triggers fired BEFORE can return null to signal the trigger manager to skip the rest of the operation for this row (i.e., subsequent triggers are not fired, and the INSERT/UPDATE/DELETE does not occur for this row).
So RETURN NULL after the UPDATE statement inside the if andRETURN NEW when the if is false. Then the INSERT will happen if the name is unique.
I have a very simple trigger, that updates a column in table_a whenever table_b is updated:
create or replace function trigger_update_status()
returns trigger as
$body$
begin
-- UPDATE TABLE A
update table_a
set a_status = new.b_status,
date_updated = now()
from table_b
where table_a.serial_number = table_b.serial_number;
return new;
end;
$body$
language plpgsql;
create trigger "currentStatus" after update or insert on table_b
for each row
execute procedure trigger_update_status();
However, I am getting the error that there is no RETURN value:
ERROR: control reached end of trigger procedure without RETURN
I'm confused on whether or not NEW is appropriate here as I've been reading conflicting information.
On the one hand, the answer here (Postgres trigger after insert accessing NEW) makes it clear that: "The return value of a row-level trigger fired AFTER or a statement-level trigger fired BEFORE or AFTER is always ignored; it might as well be null. However, any of these types of triggers might still abort the entire operation by raising an error."
On the other hand, my trigger here essentially matches the one here (https://dba.stackexchange.com/questions/182678/postgresql-trigger-to-update-a-column-in-a-table-when-another-table-gets-inserte), which calls NEW & AFTER together. So I am not sure why mine is not working. Any help is very greatly appreciated!
Future answer for anybody with same issue: it was a second (similarly named, which is why I didn't catch it until much later) trigger that was called AFTER this one that was causing the issue. The second trigger could not RETURN NEW because in this case, there was no new value. I fixed this by adding an IF/ELSE statement to my second trigger:
IF NEW.current_location <> OLD.current_location
THEN
INSERT INTO table_x(serial_number, foo, bar)
VALUES(OLD.serial_number, OLD.foo, old.bar);
return new;
-- ADDED THIS LINE:
else return null;
END IF;
Lesson learned thanks to #sticky bit - if the trigger works in an isolated dbfiddle, it's something else causing the issue.
Can someone tell me how can I check a specific column value before deleting from a table in postgreSQL?
My current code:
CREATE OR REPLACE FUNCTION f_tr_table_row_prohibit_delete() RETURNS TRIGGER AS
$$
BEGIN
IF (OLD.table_state_code=0) THEN
DELETE FROM mytable WHERE table_code=OLD.table_code;
ELSE
RAISE EXCEPTION 'The deletion of a row is allowed only when table state code is 0!';
END IF;
END;
$$
CREATE TRIGGER tr_table_row_prohibit_delete
BEFORE DELETE ON mytable
FOR EACH ROW
EXECUTE PROCEDURE f_tr_laua_rida_prohibit_delete();
LANGUAGE plpgsql SECURITY DEFINER STABLE
SET search_path = public, pg_temp;
I have a table named mytable with columns table_code and table_state_code.
Before deleteing from, mytable I want to check if the table_state_code is 0, if not then it should not allow delete if it is anything else then it should delete the row.
With my current code, it correctly raises the exception when table_state_code is not 0 but when it is then it says :
ERROR: DELETE is not allowed in a non-volatile function, instead of deleteing the row.
Thanks in advance.
In BEFORE DELETE trigger you can cancel the deletion or let it happen.
To cancel deletion you can return NULL or RAISE EXCEPTION.
To let the deletion to be continued return OLD.
The deletion has already started (as it is BEFORE DELETE trigger) so you don't have to execute DELETE FROM mytable WHERE table_code=OLD.table_code;.
See Overview of Trigger Behavior in the documentation.
I have a table with 3 fields
id, name , value
I want to add a 4th colum calcValue. The calculation of calcValue is based on the filed value in the whole table, changing it in one row can cause changes in all of the others.
I want to write a trigger that updates calcValue everytime there is insert, delete or update in the table.
What i'm worry about is that the trigger itself is going to have an Update command. Will it case another call to this trigger? Will I be stuck with infinte loop?
To describe it better:
CREATE TRIGGER x
AFTER INSERT OR UPDATE OR DELETE
ON a
FOR EACH ROW
EXECUTE PROCEDURE dosomething();
and:
CREATE OR REPLACE FUNCTION dosomething()
RETURNS trigger AS
$BODY$
begin
code + calculation of result...
for row in
QUERY
Loop
Update a set calValue=result where id=...
end loop;
end;
$BODY$
LANGUAGE plpgsql VOLATILE
Will the update of a in dosomething() will cause another invoke of the trigger x? If it does is there a way to handle it so it won't stuck in infinte loop?
My goal is to do dosomething() once per update/insert/delete action of a . I don't want dosomething() to be called again because of the update a in the trigger.
Edit: Since i'm updating in the trigger a diffrent column I can do that:
CREATE TRIGGER x
BEFORE UPDATE OF value ON a
FOR EACH ROW
EXECUTE PROCEDURE dosomething();
this should solve my problem as the trigger updates calcValue and the tigger isn't set invoke on value column. However I would still like to know if there is an answer to my original question... suppose that the trigger would have update the same column.
Another alternative would be to add a when clause, along the lines of:
CREATE TRIGGER x
AFTER INSERT OR UPDATE OR DELETE
ON a
FOR EACH ROW
WHEN NEW IS NULL OR OLD IS NULL OR NEW.value <> OLD.value
EXECUTE PROCEDURE dosomething();
It will only execute the trigger when there's a change in the value field. Therefore when inside the trigger you update calcValue, the trigger is not called again, preventing an infinite "loop".
I want to write a Postgres SQL trigger that will basically find if a number appears in a column 5 or more times. If it appears a 5th time, I want to throw an exception. Here is how the table looks:
create table tab(
first integer not null constraint pk_part_id primary key,
second integer constraint fk_super_part_id references bom,
price integer);
insert into tab values(1,NULL,100), (2,1,50), (3,1,30), (4,2,20), (5,2,10), (6,3,20);
Above are the original inserts into the table. My trigger will occur upon inserting more values into the table.
Basically if a number appears in the 'second' column more than 4 times after inserting into the table, I want to raise an exception. Here is my attempt at writing the trigger:
create function check() return trigger as '
begin
if(select first, second, price
from tab
where second in (
select second from tab
group by second
having count(second) > 4)
) then
raise exception ''Error, there are more than 5 parts.'';
end if;
return null;
end
'language plpgsql;
create trigger check
after insert or update on tab
for each row execute procedure check();
Could anyone help me out? If so that would be great! Thanks!
CREATE FUNCTION trg_upbef()
RETURN trigger as
$func$
BEGIN
IF (SELECT count(*)
FROM tab
WHERE second = NEW.second ) > 3 THEN
RAISE EXCEPTION 'Error: there are more than 5 parts.';
END IF;
RETURN NEW; -- must be NEW for BEFORE trigger
END
$func$ LANGUAGE plpgsql;
CREATE TRIGGER upbef
BEFORE INSERT OR UPDATE ON tab
FOR EACH ROW EXECUTE procedure trg_upbef();
Major points
Keyword is RETURNS, not RETURN.
Use the special variable NEW to refer to the newly inserted / updated row.
Use a BEFORE trigger. Better skip early in case of an exception.
Don't count everything for your test, just what you need. Much faster.
Use dollar-quoting. Makes your live easier.
Concurrency:
If you want to be absolutely sure, you'll have to take an exclusive lock on the table before counting. Else, concurrent inserts / updates might outfox each other under heavy concurrent load. While this is rather unlikely, it's possible.