ALTER TABLE table_a
ADD CONSTRAINT fkey
FOREIGN KEY (f_id) REFERENCES table_b(id)
ON DELETE SET NULL;
This is a normal constraint, when a tuple is deleted from table_b, a corresponding tuple's column f_id in table_a will be set to null.
Here besides set f_id to null, I want to set f_id's old value to column f_old_id. Is it possible?
Here is a trigger-based solution.
create or replace function fkey_tf() returns trigger language plpgsql as
$$
begin
update table_a
set f_old_id = f_id, f_id = null
where f_id = OLD.id;
return null;
end;
$$;
create trigger fkey_t
after delete on table_b
for each row execute procedure fkey_tf();
Please note that an index on table_a.f_id is needed in order to not sacrifice performance. This is a good practice for foreign keys anyway.
Related
#PostgreSQL 10.22
Lets say I have a table and a view of it such as in:
CREATE TABLE item
(
id integer Not Null,
name varchar(50) Not Null
);
CREATE OR REPLACE VIEW all_items AS(
SELECT i.id
FROM item i
)
WITH CHECK OPTION
When I try to insert a tuple to all_items view I get an error because of the 'Not Null' constraint on the base table. Eg:
INSERT INTO all_items
VALUES (999)
ERROR: null value in column "name" violates not-null constraint
DETAIL: Failing row contains (999, null).
I tried to use triggers in order for it to work but it didn't:
CREATE OR REPLACE FUNCTION fill_NULL_attributes()
RETURNS trigger AS $$
BEGIN
IF NEW.name IS NULL THEN
NEW.name := 'X'; -- fills empty attribute with some value
END IF;
RETURN NEW;
END;
$$ LANGUAGE plpgsql
CREATE TRIGGER all_items_insert_fix
INSTEAD OF INSERT ON all_items
FOR EACH ROW
EXECUTE PROCEDURE fill_NULL_attributes();
This trigger solution didn't work because NEW doesn't have the "name" attribute.
Is there any way of doing this?
Your trigger function would be correct in a BEFORE trigger, since it modifies the row you are about to insert. But that is not correct in an INSTEAD OF trigger: there, you have to perform the INSERT into the base table yourself.
I wanted to have an explanation on triggers of Postgres views.
To make clear what I want to ask, I'll give you a very simplified example of my case.
In this example we have two tables (table_a, table_b) that joined together make the view in the example (vw_table_ab).
In this example I will use trivial names and simple DDLs/DMLs.
-- TABLE table_a
CREATE TABLE table_a
(
id serial PRIMARY KEY,
timestamp_field timestamp DEFAULT now() NOT NULL,
boolean_field boolean DEFAULT FALSE NOT NULL
);
-- TABLE table_b
CREATE TABLE table_b
(
id serial PRIMARY KEY,
timestamp_field timestamp DEFAULT now() NOT NULL,
boolean_field boolean DEFAULT FALSE NOT NULL,
id_table_a integer NOT NULL,
CONSTRAINT "fk_table_a" FOREIGN KEY (id_table_a) REFERENCES table_a (id) ON DELETE CASCADE NOT DEFERRABLE,
CONSTRAINT "u_table_a" UNIQUE (id_table_a)
);
-- VIEW vw_table_ab
CREATE VIEW vw_table_ab AS (
SELECT a.timestamp_field AS timestamp_a,
a.boolean_field AS boolean_a,
b.timestamp_field AS timestamp_b,
b.boolean_field AS boolean_b
FROM table_a a
JOIN table_b b ON a.id = b.id_table_a
);
A trigger function on standard actions (INSERT, UPDATE and DELETE) is linked to this view through an INSTEAD OF trigger.
-- TRIGGER FUNCTION fn_trigger
CREATE FUNCTION fn_trigger() RETURNS trigger LANGUAGE plpgsql AS
$_$
DECLARE
sql TEXT;
BEGIN
sql = 'SELECT ' || TG_TABLE_NAME || '_' || lower(TG_OP) || '($1);';
IF TG_OP = 'INSERT' OR TG_OP = 'UPDATE' THEN
EXECUTE (sql) USING NEW;
RAISE NOTICE '%', sql;
RETURN NEW;
ELSE
EXECUTE (sql) USING OLD;
RAISE NOTICE '%', sql;
RETURN OLD;
END IF;
END;
$_$;
-- TRIGGER tr_table_ab
CREATE TRIGGER tr_table_ab
INSTEAD OF INSERT OR UPDATE OR DELETE ON vw_table_ab
FOR EACH ROW EXECUTE PROCEDURE fn_trigger();
The example I bring has a trigger called only on the insert action, and the function that is executed is this:
-- INSERT FUNCTION vw_table_ab_insert
CREATE FUNCTION vw_table_ab_insert(new vw_table_ab) RETURNS void LANGUAGE plpgsql AS
$_$
DECLARE
id_table_a integer;
BEGIN
INSERT INTO table_a (timestamp_field, boolean_field) VALUES (new.timestamp_a, new.boolean_a)
RETURNING id
INTO id_table_a;
INSERT INTO table_b (timestamp_field, boolean_field, id_table_a) VALUES (new.timestamp_a, new.boolean_b, id_table_a);
END;
$_$;
Now we can get to my problem. I make an insert on the view, and when the action is triggered, I get a "Not null violation" error becouse I have some NOT NULL constraints on table_a and table_b like in this case:
INSERT INTO vw_table_ab (timestamp_a, boolean_a, timestamp_b, boolean_b) VALUES (now(), NULL, now(), NULL);
Suppose that the previous statement is generated through a programming language framework and I don't want to handle this case in backend code, but I want handle this case in PostgreSQL in the insert function vw_table_ab_insert. So at this point my problem is bound to the new parameter of the function because I have fields of the view that are NULL. But these fields have a DEFAULT value in the definition of the base table, and I want to use that.
...
timestamp_field timestamp DEFAULT now() NOT NULL,
boolean_field boolean DEFAULT FALSE NOT NULL
...
My question:
How can I manage the NULL values in trigger of the views using the DEFAULT defined in the tables?
Initially I thought of putting IF ... THEN ... inside the function and override null values with DEFAULT expression but I do not really like that.
For example, the function would become like this:
CREATE FUNCTION vw_table_ab_insert(new vw_table_ab) RETURNS void LANGUAGE plpgsql AS
$_$
DECLARE
id_table_a integer;
BEGIN
IF new.timestamp_a IS NULL THEN
new.timestamp_a = DEFAULT;
END IF;
IF new.boolean_a IS NULL THEN
new.boolean_a = DEFAULT;
END IF;
IF new.timestamp_b IS NULL THEN
new.timestamp_b = DEFAULT;
END IF;
IF new.boolean_b IS NULL THEN
new.boolean_b = DEFAULT;
END IF;
INSERT INTO table_a (timestamp_field, boolean_field)
VALUES (new.timestamp_a, new.boolean_a)
RETURNING id
INTO id_table_a;
INSERT INTO table_b (timestamp_field, boolean_field, id_table_a)
VALUES (new.timestamp_a, new.boolean_b, id_table_a);
END;
$_$;
Someone can help me? Is there another method for handling this case?
The easiest way would be to use ALTER VIEW ... ALTER col SET DEFAULT to define default values on the view that are the same as the default values on the base table.
Then instead of inserting explicit NULLs, omit the columns from the INSERT statement or insert DEFAULT explicitly. Your resulting view will behave just like a real table.
I'm having difficulties in this simple trigger. My purpose is to verify before inserting a new register if is there's a register with the same field content which is "tag_id". If NEW tag_id is the same tag_id of any register on my table "coordenadas", then it updates, if not, it inserts a new one. When I try to insert sth, I get the error:
ERROR: record "old" is not assigned yet
DETAIL: The tuple structure of a not-yet-assigned record is indeterminate.
CONTEXT: PL/pgSQL function verifica_coo() line 7 at IF
I have this table:
CREATE TABLE public.coordenadas
(
id bigint NOT NULL,
pos_data timestamp without time zone,
pos_latitude double precision,
pos_longitude double precision,
tag_id bigint NOT NULL,
gado_id bigint NOT NULL,
CONSTRAINT coordenadas_pkey PRIMARY KEY (id),
CONSTRAINT coordenadas_gado_id_fkey FOREIGN KEY (gado_id)
REFERENCES public.gado (gado_id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION,
CONSTRAINT fkj14dwmpa6g037ardymqc2q4lj FOREIGN KEY (tag_id)
REFERENCES public.tag (tag_id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION,
CONSTRAINT fktawrw6tlliq4ace5p7io87c5p FOREIGN KEY (gado_id)
REFERENCES public.gado (gado_id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION
)
This trigger:
CREATE TRIGGER verifica_coo
BEFORE INSERT OR UPDATE ON coordenadas
FOR EACH ROW EXECUTE PROCEDURE verifica_coo();
This function:
CREATE OR REPLACE FUNCTION public.verifica_coo()
RETURNS trigger AS $verifica_coo$
BEGIN
--
-- Verifica se é para inserir ou atualizar os dados na tabela.
--
IF (NEW.tag_id != OLD.tag_id ) THEN
INSERT INTO coordenadas (pos_data,pos_latitude,pos_longitude,tag_id,gado_id)
VALUES (NEW.pos_data,NEW.pos_latitude,NEW.pos_longitude,NEW.tag_id,NEW.gado_id);
ELSE
UPDATE coordenadas SET pos_data = NEW.pos_data, pos_latitude = NEW.pos_latitude, pos_longitude = NEW.pos_longitude WHERE tag_id = NEW.tag_id;
END IF;
RETURN NEW;
END;
$verifica_coo$
LANGUAGE plpgsql VOLATILE
COST 100;
ALTER FUNCTION public.verifica_coo()
OWNER TO postgres;
My insert:
INSERT INTO coordenadas (pos_data,pos_latitude,pos_longitude,tag_id,gado_id) VALUES ('21/08/2016', '-23.563844' ,'-46.322525', '2','2');
This is because:
OLD
Data type RECORD; variable holding the old database row for
UPDATE/DELETE operations in row-level triggers. This variable is
unassigned in statement-level triggers and for INSERT operations.
So you first need to check if you are doing an insert or update. That information is available in TG_OP
IF TG_OP = 'UPDATE' THEN
-- some code involving OLD
ELSE
-- other code
I have a trigger function that copy row of unique values to another table on update or insert that ALMOST work.
The trigger should only insert a new row to the sample table if the number don't exist in it before. Atm. it insert a new row to the sample table with the value NULL if the number already exist in the table. I dont want it to do anything if maintbl.number = sample.nb_main
EDIT: sample table and sample data
CREATE TABLE schema.main(
sid SERIAL NOT NULL,
number INTEGER,
CONSTRAINT sid_pk PRIMARY KEY (sid)
)
CREATE TABLE schema.sample(
gid SERIAL NOT NULL,
nb_main INTEGER,
CONSTRAINT gid_pk PRIMARY KEY (gid)
Example and desired result
schema.main schema.sample
number nb_main
234233 234233
234234 555555
234234
555555
555555
CREATE OR REPLACE FUNCTION schema.update_number()
RETURNS trigger AS
$BODY$
BEGIN
INSERT INTO schema.sample(
nb_main)
SELECT DISTINCT(maintbl.number)
FROM schema.maintbl
WHERE NOT EXISTS (
SELECT nb_main FROM schema.sample WHERE maintbl.number = sample.nb_main);
RETURN NEW;
END;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
ALTER FUNCTION schema.update_number()
OWNER TO postgres;
CREATE TRIGGER update_number
AFTER INSERT OR UPDATE
ON schema.maintbl
FOR EACH ROW
EXECUTE PROCEDURE schema.update_number();
I just found out that my select query is probably wrong, if I run SELECT query by itself it return one row 'NULL' but i should not?
SELECT DISTINCT(maintbl.number)
FROM schema.maintbl
WHERE NOT EXISTS (
SELECT nb_main FROM schema.sample WHERE maintbl.number = sample.nb_main);
Any good advice?
Best
If I understood correctly, you wish to append to schema.sample a number that has been inserted or updated in schema.maintbl, right?
CREATE OR REPLACE FUNCTION schema.update_number()
RETURNS trigger AS
$BODY$
BEGIN
IF (SELECT COUNT(*) FROM schema.sample WHERE number = NEW.number) = 0 THEN
INSERT INTO schema.sample(nb_main) VALUES (NEW.number);
END IF;
RETURN NEW;
END;
$BODY$
LANGUAGE plpgsql VOLATILE;
I would like to add a constraint that will check values from related table.
I have 3 tables:
CREATE TABLE somethink_usr_rel (
user_id BIGINT NOT NULL,
stomethink_id BIGINT NOT NULL
);
CREATE TABLE usr (
id BIGINT NOT NULL,
role_id BIGINT NOT NULL
);
CREATE TABLE role (
id BIGINT NOT NULL,
type BIGINT NOT NULL
);
(If you want me to put constraint with FK let me know.)
I want to add a constraint to somethink_usr_rel that checks type in role ("two tables away"), e.g.:
ALTER TABLE somethink_usr_rel
ADD CONSTRAINT CH_sm_usr_type_check
CHECK (usr.role.type = 'SOME_ENUM');
I tried to do this with JOINs but didn't succeed. Any idea how to achieve it?
CHECK constraints cannot currently reference other tables. The manual:
Currently, CHECK expressions cannot contain subqueries nor refer to
variables other than columns of the current row.
One way is to use a trigger like demonstrated by #Wolph.
A clean solution without triggers: add redundant columns and include them in FOREIGN KEY constraints, which are the first choice to enforce referential integrity. Related answer on dba.SE with detailed instructions:
Enforcing constraints “two tables away”
Another option would be to "fake" an IMMUTABLE function doing the check and use that in a CHECK constraint. Postgres will allow this, but be aware of possible caveats. Best make that a NOT VALID constraint. See:
Disable all constraints and table checks while restoring a dump
A CHECK constraint is not an option if you need joins. You can create a trigger which raises an error instead.
Have a look at this example: http://www.postgresql.org/docs/9.1/static/plpgsql-trigger.html#PLPGSQL-TRIGGER-EXAMPLE
CREATE TABLE emp (
empname text,
salary integer,
last_date timestamp,
last_user text
);
CREATE FUNCTION emp_stamp() RETURNS trigger AS $emp_stamp$
BEGIN
-- Check that empname and salary are given
IF NEW.empname IS NULL THEN
RAISE EXCEPTION 'empname cannot be null';
END IF;
IF NEW.salary IS NULL THEN
RAISE EXCEPTION '% cannot have null salary', NEW.empname;
END IF;
-- Who works for us when she must pay for it?
IF NEW.salary < 0 THEN
RAISE EXCEPTION '% cannot have a negative salary', NEW.empname;
END IF;
-- Remember who changed the payroll when
NEW.last_date := current_timestamp;
NEW.last_user := current_user;
RETURN NEW;
END;
$emp_stamp$ LANGUAGE plpgsql;
CREATE TRIGGER emp_stamp BEFORE INSERT OR UPDATE ON emp
FOR EACH ROW EXECUTE PROCEDURE emp_stamp();
...i did it so (nazwa=user name, firma = company name) :
CREATE TABLE users
(
id bigserial CONSTRAINT firstkey PRIMARY KEY,
nazwa character varying(20),
firma character varying(50)
);
CREATE TABLE test
(
id bigserial CONSTRAINT firstkey PRIMARY KEY,
firma character varying(50),
towar character varying(20),
nazwisko character varying(20)
);
ALTER TABLE public.test ENABLE ROW LEVEL SECURITY;
CREATE OR REPLACE FUNCTION whoIAM3() RETURNS varchar(50) as $$
declare
result varchar(50);
BEGIN
select into result users.firma from users where users.nazwa = current_user;
return result;
END;
$$ LANGUAGE plpgsql;
CREATE POLICY user_policy ON public.test
USING (firma = whoIAM3());
CREATE FUNCTION test_trigger_function()
RETURNS trigger AS $$
BEGIN
NEW.firma:=whoIam3();
return NEW;
END
$$ LANGUAGE 'plpgsql'
CREATE TRIGGER test_trigger_insert BEFORE INSERT ON test FOR EACH ROW EXECUTE PROCEDURE test_trigger_function();