I have been trying to write a trigger function that updates the rows in the child table when the parent is changed for a while now.
I have read Trigger procedure documentation but i have not really grasped how to build the functions.
This is what I have tried that does not work...
CREATE FUNCTION myschema.update_child() RETURNS trigger AS
$BODY$
BEGIN
UPDATE myschema.child
set new.number = parent.number
FROM myschema.parent
WHERE id = "id";
RETURN NEW;
END
$BODY$
LANGUAGE plpgsql
Then the trigger
CREATE TRIGGER update_child_after_update
AFTER INSERT OR UPDATE OR DELETE
ON myschema.child
FOR EACH ROW
EXECUTE PROCEDURE myschema.update_child();
Does anyone have some tips to give?
Best regards
You don't need to use the parent table in the body of the trigger function, because the values from the parent table are available in the function in the special variable OLD and NEW. In this case you only need NEW.
If you need the trigger only on update, than define a update-only trigger:
CREATE or replace FUNCTION update_child() RETURNS trigger AS
$BODY$
BEGIN
UPDATE child
set number = NEW.number
WHERE id = NEW.id;
RETURN NEW;
END
$BODY$
LANGUAGE plpgsql;
CREATE TRIGGER update_child_after_update
AFTER UPDATE
ON parent
FOR EACH ROW
EXECUTE PROCEDURE update_child();
Related
I am trying to create a trigger and procedure to update a last_changed_timestamp column upon UPDATE and INSERT.
I can register the function and trigger just fine, but when I try to update a record I receive the error.
CREATE OR REPLACE FUNCTION update_my_table_last_changed_timestamp()
RETURNS trigger AS
$BODY$
BEGIN
UPDATE my_table SET NEW.last_changed_timestamp = NOW();
RETURN NEW;
END;
$BODY$
LANGUAGE plpgsql;
CREATE TRIGGER trigger_update_my_table_last_changed_timestamp
BEFORE UPDATE
ON my_table
FOR EACH ROW
EXECUTE PROCEDURE update_my_table_last_changed_timestamp();
column "new" of relation "my_table" does not exist
I also do not fully understand how update_my_table_last_changed_timestamp knows which row it's suppose to update, nor if there were parameters passed to it, how the I would get those variables from the trigger to the procedure.
Modify the NEW record, there is no need to update.
BEGIN
NEW.last_changed_timestamp = NOW();
RETURN NEW;
END;
Read in the documentation: Overview of Trigger Behavior
If you still want to access a (other )table in the update trigger.
You can add to beginning of your trigger body the following:
EXECUTE format('SET search_path TO %I', TG_TABLE_SCHEMA);
For some reason with the update trigger it can happen that you're not on the correct search_path (i believe some old psql version have this)
I wrote the following trigger:
CREATE FUNCTION trig_func() RETURNS trigger AS $$
BEGIN
IF NEW = OLD
THEN -- update would do nothing, doing something...
END IF;
RETURN NEW;
END;
$$ LANGUAGE plpgsql;
CREATE TRIGGER trig BEFORE UPDATE ON some_table
FOR EACH ROW EXECUTE PROCEDURE trig_func();
It makes it clear what I'd like to achieve, but what is the proper thing to put in place of NEW = OLD?
The is distinct from operator can compare complete rows and will handle nulls correctly.
So you want
if new is not distinct from old then
...
end if;
I want to create a trigger which counts rows and updates a field in an other table. My current solution works for INSERT statements but failes when I DELETE a row.
My current function:
CREATE OR REPLACE FUNCTION update_table_count()
RETURNS trigger AS
$$
DECLARE updatecount INT;
BEGIN
Select count(*) into updatecount
From source_table
Where id = new.id;
Update dest_table set count=updatecount
Where id = new.id;
RETURN NEW;
END;
$$
LANGUAGE 'plpgsql';
The trigger is a pretty basic one, looking like.
CREATE TRIGGER count_trigger
AFTER INSERT OR DELETE
ON source_table
FOR EACH ROW
EXECUTE PROCEDURE update_table_count();
When I excute a DELETE statement the following error occurs:
ERROR: record "new" is not assigned yet
DETAIL: The tuple structure of a not-yet-assigned record is indeterminate.
I know one solution could be to create just one set of trigger and function for the DELETE and one for the INSERT statement. But I want to do it a bit more elegant and want to know, if there is a solution to check if NEW or OLD is present in the current context and just implement an IF ELSE block. But I dont know how to check for this context sensitive items.
Thanks for your help
The usual approach to make a trigger function do different things depending on how the trigger was fired is to check the trigger operation through TG_OP
CREATE OR REPLACE FUNCTION update_table_count()
RETURNS trigger AS
$$
DECLARE
updatecount INT;
BEGIN
if tg_op = 'UPDATE' then
select count(*) into updatecount from source_table where id = new.id;
update dest_table set count=updatecount where id = new.id;
elsif tg_op = 'DELETE' then
... do something else
end if;
RETURN NEW;
END;
$$
LANGUAGE plpgsql;
Unrelated, but: the language name is an identifier. Do not quote it using single quotes.
From PostgreSQL's documentation:
NEW
Data type RECORD; variable holding the new database row for INSERT/UPDATE operations in row-level triggers. This variable is null in statement-level triggers and for DELETE operations.
OLD
Data type RECORD; variable holding the old database row for UPDATE/DELETE operations in row-level triggers. This variable is null in statement-level triggers and for INSERT operations.
So, for example, if NEW is NULL, then the trigger was invoked on DELETE.
The code below is my code to create trigger function to change column "pass".
create or replace function change_pass()
returns trigger as
$$
begin
NEW.pass := 'XXXXXXXXX';
return NEW;
end
$$
language plpgsql;
create trigger change_pass
AFTER insert or update on "D_ACCOUNT"
for each row execute procedure change_pass();
When i called insert, i did not see any changes in my data.
Can anyone explain to me where i was wrong?
You need a BEFORE trigger to change values in the NEW record:
create trigger change_pass
BEFORE insert or update on "D_ACCOUNT"
for each row execute procedure change_pass();
I've been playing around for the last hour or more trying to put an update statement into a trigger. I understand the concept of an UPDATE statement and the below works just fine
UPDATE cars SET country = 'France';
What I want is to put this into a trigger so that when the cars table is updated, the column country will automatically be updated with France.
I've played around with adapting Functions and Triggers that I've found out on the interweb but I'm obviously making the statement wrong as either they don't execute or they execute but don't update the country field when a new record is added.
CREATE FUNCTION update_country () RETURNS TRIGGER AS $$
BEGIN
IF (TG_OP = 'UPDATE') THEN
UPDATE cars SET country = 'France' WHERE id = New.id;
END IF;
RETURN NULL;
END;
$$ LANGUAGE plpgsql; --The trigger used to update a table.
CREATE TRIGGER update_country_col BEFORE UPDATE ON cars FOR EACH ROW EXECUTE PROCEDURE update_country();
The above scripts executes but does not add France to the country column.
The function was adapted from a statement that I found out on the web.
Postgres 9.1.
I know that the answer is going to be so simple!
In update triggers you should modify NEW record.
Also, you may need to return NEW record from procedure.
So, you should use following procedure instead of yours:
CREATE FUNCTION update_country () RETURNS TRIGGER AS $$
BEGIN
IF (TG_OP = 'UPDATE') THEN
NEW.country = 'France';
END IF;
RETURN NEW;
END; $$ LANGUAGE plpgsql;