I'm brand new. The task was to create a trigger that will delete all dependent tuples from the depositor table when an account in a parent table is deleted. Here's what I've got so far. I keep getting a syntax error "at or near 'cust_id'" and I can't find it. Can you tell me if this trigger will do what I'm wanting it to do (delete the cust_id and account_number from the depositor table for the account that was deleted in the account table) and help me find the syntax error?
CREATE OR REPLACE FUNCTION Froehle_13_bankTriggerFunction()
RETURNS TRIGGER
LANGUAGE plpgsql
AS
$$
BEGIN
DELETE cust_id, account_number
FROM depositor
WHERE depositor.account_number = account.account_number;
END;
$$;
You need to make 3 changes:
Fix the delete statement syntax error by removing the columns. It must be just delete from table where ...
Replace account with the special keyword old, which refers to the row being deleted
Add a return statement, which is required for all trigger functions
Try this:
CREATE OR REPLACE FUNCTION Froehle_13_bankTriggerFunction()
RETURNS TRIGGER
LANGUAGE plpgsql
AS
$$
BEGIN
DELETE FROM depositor
WHERE depositor.account_number = OLD.account_number;
RETURN NULL;
END;
$$;
There is a final simplification you can make: Delete the entire function and instead alter the references constraint on the account_number column of depositor to add ON DELETE CASCADE.
Related
I'm new to PostgreSQL and really loving how constraints work with row level security, but I'm confused how to make them do what I want them to.
I have a column and I want add a constraint that creates a minimum length for a text column, this check works for that:
(length((column_name):: text) > 6)
BUT, it also then prevents users updating any rows where column_name is already under 6 characters.
I want to make it so they can't change that value TO that, but can still update a row where that is already happening, so they can change it as needed according to my new policy.
Is this possible?
BUT, it also then prevents users updating any rows where column_name is already under 6 characters.
Well, no. When you try to add that CHECK constraint, all existing rows are checked, and an exception is raised if any violation is found.
You would have to make it NOT VALID. Then yes.
You really need a trigger on INSERT or UPDATE that checks new values. Not as cheap and not as bullet-rpoof, but still pretty solid. Like:
CREATE OR REPLACE FUNCTION trg_col_min_len6()
RETURNS trigger
LANGUAGE plpgsql AS
$func$
BEGIN
IF TG_OP = 'UPDATE'
AND OLD.column_name IS NOT DISTINCT FROM NEW.column_name THEN
-- do nothing
ELSE
RAISE EXCEPTION 'New value for column "note" must have at least 6 characters.';
END IF;
RETURN NEW;
END
$func$;
-- trigger
CREATE TRIGGER tbl1_column_name_min_len6
BEFORE INSERT OR UPDATE ON tbl
FOR EACH ROW
WHEN (length(NEW.column_name) < 7)
EXECUTE FUNCTION trg_col_min_len6();
db<>fiddle here
It should be most efficient to check in a WHEN condition to the trigger directly. Then the trigger function is only ever called for short values and can be super simple.
See:
Trigger with multiple WHEN conditions
Fire trigger on update of columnA or ColumnB or ColumnC
You can create separate triggers for Insert and Update letting each completely define when it should fired. If completely different logic is required for the DML action this technique allows writing dedicated trigger functions. In this case that is not required the trigger function reduces to raise exception .... See Demo
-- Single trigger function for both Insert and Delete
create or replace function trg_col_min_len6()
returns trigger
language plpgsql
as $$
begin
raise exception 'Cannot % val = ''%''. Must have at least 6 characters.'
, tg_op, new.val;
return null;
end;
$$;
-- trigger before insert
create trigger tbl_val_min_len6_bir
before insert
on tbl
for each row
when (length(new.val) < 6)
execute function trg_col_min_len6();
-- trugger before update
create trigger tbl_val_min_len6_bur
before update
on tbl
for each row
when ( length(new.val) < 6
and new.val is distinct from old.val
)
execute function trg_col_min_len6();
I created a table name Student in PostgreSQL and then I tried defining a trigger on that table but it's showing an error message in doing so.
Trigger Syntax:
CREATE TRIGGER bi_Student BEFORE INSERT ON Student as $$
FOR EACH ROW
BEGIN
raise notice 'Successfully inserted into table(%)', user;
end $$;
Table Creation Command:
create table Student(Stu_id int, Stu_Name text, Stu_Age int, Stu_address char(30));
Actually I tried to declare the execution statements directly inside the trigger only rather than calling any procedure/ function from the trigger which is working fine but I want to do in this way in PostgreSQL.
PostgreSQL doesn't support it. You need trigger function always.
As documented in the manual you need a trigger function
create function my_trigger_function()
returns trigger
as
$$
begin
raise notice 'Successfully inserted into table(%)', user;
return new; --<< important (see the manual for details)
end
$$
language plpgsql;
Not sure what you intend with the user parameter there, as that is not the table name, but the current database user. If you want to display the actual table name, you need to use TG_RELNAME instead - which is an implicit variable available in the trigger function.
And a trigger definition
CREATE TRIGGER bi_Student
BEFORE INSERT ON Student
FOR EACH ROW
execute function my_trigger_function();
I have an already made table:
cotizacion(idCot(PK), unit_price,unit_price_taxes)
I need to convert unit_price_taxes into a generated column that is equal to unit_price*1.16. The issue is I can't find the alter table statement which will give me this. Dropping table and creating it again is not an option as this table is already deeply linked with the rest of the database and reinserting all records is not an option at this point.
I tried the following:
ALTER TABLE cotizacion
alter column unit_price_taxes set
GENERATED ALWAYS AS (unit_price*1.16) STORED;
But it's not working. Does anybody know how to get this done or if it's even possible? I would like to avoid creating a new column.
Thanks!
**EDIT:
I also tried the following trigger implementation:
CREATE OR REPLACE FUNCTION calculate_price_taxes()
RETURNS trigger
LANGUAGE plpgsql
AS $function$
declare pu money;
begin
select unit_price from cotizacion into pu
where idCot = new."idCot";
update cotizacion
set unit_price_taxes = pu * (1.16)
where idCot = new."idCot";
return new;
end;
$function$
;
And the trigger delcaration:
Create or replace trigger price_taxes
after update on cotizacion
for each row
execute procedure
calculate_price_taxes()
The most probable reason for your trigger to go into an infinite recursion is that you are running an UPDATE statement inside the trigger - which is the wrong thing to do. Create a before trigger and assign the calculated value to the new record:
create trigger update_tax()
returns trigger
as
$$
begin
new.unit_price_taxes := unit_price * 1.16;
return new;
end;
$$
language plpgsql;
create trigger update_tax_trigger()
before update or insert on cotizacion
for each row execute procedure update_tax();
The only way to "convert" that column to a generated one, is to drop it and add it again:
alter table cotizacion
drop unit_price_taxes;
alter table cotizacion
add unit_price_taxes numeric generated always as (unit_price*1.16) stored;
Note that this will rewrite the entire table which will block access to it. Adding the trigger will be less invasive.
I'm trying to create a function + trigger that will update my "modif" attribut to current date when there is an update or insert on my table called "nada".
the code work well but all the rows are affected.I only want the current date on the rows that were updated.
Any idea ?
This is my code so far:
CREATE OR REPLACE FUNCTION public.maj_modif()
RETURNS "trigger" AS
$BODY$
BEGIN
NEW.modif:= (SELECT current_date);
RETURN NEW;
END;
$BODY$
LANGUAGE plpgsql;
DROP TRIGGER IF EXISTS maj_modif ON public.nada;
CREATE TRIGGER maj_modif BEFORE INSERT OR UPDATE ON public.nada
FOR EACH ROW
EXECUTE PROCEDURE public.maj_modif();
If I try the same code without "FOR EACH ROW" in the trigger I get this erreur: « new » is not affected yet (...) The structure of the registration line is not yet determined.
I assume that you only want the trigger to fire if any columns were actually changed.
That can be done with
CREATE TRIGGER maj_modif BEFORE UPDATE ON public.nada
FOR EACH ROW
WHEN OLD <> NEW
EXECUTE PROCEDURE public.maj_modif();
That only works for UPDATE, because on INSERT OLD is not defined. Define the INSERT trigger without the WHEN clause.
I have created an before update and after update trigger on a postgresql db table.
There is a requirement to preserve historical record and at the same time create a new record for the said data. Old record is to be marked as archived.
I was planning on using temporary table to keep track of the NEW values and reset the NEW values such that it is marked as archived.
In my after update trigger I would read the data from the temporary table, and create a brand new active record.
My problem is temporary table created in before update trigger is not visible to after update trigger. Moreover I cannot even pass on any argument (of type record) to the after update trigger as it is not allowed.
I have already achieved the desired result in Oracle db, using Global Temporary table, but having a tough time in PostgreSQL.
Here is the sample code for before update trigger function:
CREATE OR REPLACE FUNCTION trigger_fct_trig_trk_beforeupdate()
RETURNS trigger AS
$BODY$
DECLARE
some variable declarations;
BEGIN
Drop table IF EXISTS track_tmp_test;
CREATE TEMPORARY TABLE track_tmp_test(
...
);
Insert into track_tmp_test (........)
values(NEW., NEW..., NEW.., NEW...);
NEW... := OLD...;
NEW... := OLD.... ;
NEW... := OLD...;
Mark the NEW.status : = 'archived';
RETURN NEW;
END
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
CREATE TRIGGER trig_trk_test_beforeupdate
BEFORE UPDATE ON test
FOR EACH ROW EXECUTE PROCEDURE trigger_fct_trig_trk_beforeupdate() ;
NOW the after UPDATE trigger function:
CREATE OR REPLACE FUNCTION trigger_fct_trg_trk_afterupdate()
RETURNS trigger AS
$BODY$
DECLARE
some variables;
-- insert into original table the data from temporary that was inserted in before update trigger
INSERT into TEST (....)
select ....
from track_tmp_test ;
-- delete data from temporary table after insert
delete from track_tmp_test ;
EXCEPTION
WHEN OTHERS THEN
-- Consider logging the error and then re-raise
RAISE;
RETURN NEW;
END
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
Is there a way that after update trigger can access the temporary table created in before update trigger function?
I cannot have a permanent table hold he values, as trigger can be fired by many users updating the data in the table.
There is no problem with access to temporary table from triggers, and following code working without issue (on PostgreSQL 9.4):
CREATE OR REPLACE FUNCTION public.f1()
RETURNS trigger
LANGUAGE plpgsql
AS $function$
begin
drop table if exists bubu;
create temp table bubu(a int);
insert into bubu values(10);
return new;
end
$function$
CREATE OR REPLACE FUNCTION public.f2()
RETURNS trigger
LANGUAGE plpgsql
AS $function$
declare r record;
begin
for r in select * from bubu
loop
raise notice '%', r;
end loop;
return null;
end
$function$
create trigger xx
before insert on omega
for each row execute procedure f1();
create trigger yy
after insert on omega
for each row execute procedure f2();
postgres=# insert into omega values(333);
NOTICE: (10)
INSERT 0 1
So I am sure, so your problem will not be in access to temporary tables. It works well. There can be a issue on some 8.2, 8.3 and older with invalid plans due reference on dropped objects. Isn't it your problem?
I can say, so your design is wrong - there is not any reason, why you have to use a temp table. Same job you can do in after trigger. Any operations inside triggers should be fast, pretty fast. Dropping or creating temporary table is not fast operation.
If you have a older PostgreSQL release, you have not to drop temp table every. You should to delete content only. See a article http://postgres.cz/wiki/Automatic_execution_plan_caching_in_PL/pgSQL
The temporary table should be visible as #Pavel explains, but that's not the main issue here.
Your approach might make sense in Oracle with a global temporary table. But the posted Postgres code does not.
The trigger is fired for each row. You would (drop and) create a temp table for every row, and call another trigger, just to do what you could easily do in one trigger directly.
Instead, to keep the old row and set it to archived, plus INSERT a copy of the NEW row:
Demo table:
CREATE TEMP TABLE test (id int, txt text, archived bool DEFAULT FALSE);
Trigger func:
CREATE OR REPLACE FUNCTION trg_test_beforeupdate()
RETURNS trigger AS
$func$
BEGIN
INSERT INTO test SELECT (NEW).*; -- insert a copy of the NEW row
SELECT (OLD).* INTO NEW; -- revert row to previous state
NEW.archived = TRUE; -- just set it to "archived"
RETURN NEW;
END
$func$ LANGUAGE plpgsql;
Trigger:
CREATE TRIGGER beforeupdate
BEFORE UPDATE ON test
FOR EACH ROW EXECUTE PROCEDURE trg_test_beforeupdate();
Test:
INSERT INTO test VALUES (1, 'foo'), (2, 'bar');
UPDATE test SET txt = 'baz' WHERE id = 1;
SELECT * FROM test;
Works.