I've got two tables, "books" and "tags". I have a third, "book_tags", that tracks which tags are given to which books. I realize there may be other setups that would work better, but let's just say it has to be this way.
books: isbn (PK), title, author, ...
tags: tag_name (PK)
book_tags: isbn (FK), tag (FK)
(isbn, tag) form PK
Is it possible to write inserts for the book_tags table in such a way that any new tags will be automatically added to the tags table?
In case it's relevant, I'm using postgres 9.6.
Yes you can use triggers on the insert query. Check this
1. Create a function that adds new record to tags table whenever a new query is executed agains book_tags.
2. Create a trigger for each row on book_tags with the above
create table books(isbn int PRIMARY KEY, title varchar, author
varchar);
create table tags(tag_name int PRIMARY KEY);
create table book_tags(isbn int references books(isbn), tag int
references tags(tag_name));
Create function addtotags()
create or replace function addtotags() returns trigger as $$
begin
insert into tags(tag_name) values(new.tag_name);
return new;
end;$$
language plpgsql;
Create a trigger execadd_to_tags:
create trigger execadd_to_tags before insert on book_tags for each row
execute procedure addtotags();
insert into books(1,'abc','x');
insert into book_tags(1,1);
I would look into postgresql's trigger functions: https://www.postgresql.org/docs/9.6/static/functions-trigger.html
You can create a trigger that whenever you insert/delete/update on a specific table you can run a function that can automatically do whatever you want.
Related
I have a trigger function:
CREATE OR REPLACE FUNCTION Day_21_bankTriggerFunction()
RETURNS TRIGGER
LANGUAGE plpgsql
AS
$$
DECLARE
act VARCHAR(30);
BEGIN
SELECT account_number INTO act
DELETE FROM depositor
WHERE depositor.account_number = act;
RETURN act;
END;
$$;
\`
and then I have a trigger:
CREATE TRIGGER Day_21_bankTrigger AFTER DELETE on account FOR EACH ROW EXECUTE PROCEDURE Day_21_bankTriggerFunction()
The thought behind this is that is an account was deleted from the account table then this should trigger the function to run and then delete all records on the depositor table where that account is present.
I can create the trigger function and trigger without an issues but if I attempt to delete an account from the account table...I still see the account # in the depositor table when I shouldn't.
Any thoughts?
above is what I tried. Expected results would be to delete an account from the account table and then the trigger function should kick off and remove that account from the depositor table
Usually, relationships of any mode between tables are created by foreign keys. This is the best way and are standards for DBs. Using foreign keys you can control your data. SQL sample:
CREATE TABLE contacts(
contact_id INT GENERATED ALWAYS AS IDENTITY,
customer_id INT,
contact_name VARCHAR(255) NOT NULL,
email VARCHAR(100),
PRIMARY KEY(contact_id),
CONSTRAINT fk_customer
FOREIGN KEY(customer_id)
REFERENCES customers(customer_id)
ON DELETE SET NULL
ON UPDATE SET NULL
);
Third, specify the parent table and parent key columns referenced by the foreign key columns in the REFERENCES clause.
Finally, specify the delete and update actions in the ON DELETE and ON UPDATE clauses.
The delete and update actions determine the behaviors when the primary key in the parent table is deleted and updated. Since the primary key is rarely updated, the ON UPDATE action is not often used in practice. We’ll focus on the ON DELETE action.
PostgreSQL supports the following actions after updating or deleting:
SET NULL (Set values to NULL if data exists on referencing table)
SET DEFAULT (Set values to DEFAULT VALUES of this field if data exists on referencing table)
RESTRICT (Similar to NO ACTION)
NO ACTION (Can not update or delete data if exists on referencing table)
CASCADE (Delete all data if exists on referencing table)
I wrote for you a sample trigger function:
CREATE OR REPLACE FUNCTION Day_21_bankTriggerFunction()
RETURNS trigger
LANGUAGE plpgsql
AS $function$
declare
act varchar(30);
begin
-- get account_number from deleted record
act = old.account_number;
-- SECTION-1 :: Protect deleting if existing data
if (exists(select 1 from depositor where account_number = act)) then
return null;
end if;
-- SECTION-1 :: END
-- SECTION-2 :: Delete all data in the anothers table if exists */
delete from depositor where account_number = act;
return old;
-- SECTION-2 :: END
end
$function$;
CREATE TRIGGER Day_21_bankTrigger
BEFORE DELETE on account
FOR EACH ROW EXECUTE PROCEDURE Day_21_bankTriggerFunction();
Inside my trigger function, I have written two types of SQL codes. (SECTION-1, SECTION-2). You must choose one of them.
in my simple application I would like to create a view in order to allow users filling data of my db.
Here a little example of my data
CREATE TABLE specie
(
specie_id INT PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY,
nome_comune TEXT UNIQUE,
nome_scientifico TEXT UNIQUE
);
CREATE TABLE rilevatore
(
rilevatore_id INT PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY,
nome_cognome TEXT UNIQUE,
telefono INTEGER,
email TEXT,
ente_appartenenza TEXT
);
CREATE TABLE evento_investimento
(
evento_id INT PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY,
data DATE,
ora TIME WITHOUT TIME ZONE,
rilevatore_id INT REFERENCES rilevatore (rilevatore_id),
specie_id INT REFERENCES specie(specie_id),
);
This is the VIEW I created
CREATE VIEW investimenti_vista AS
SELECT
evento_investimento.evento_id,
evento_investimento.ora,
evento_investimento.data,
rilevatore.nome_cognome,
rilevatore.telefono,
rilevatore.email,
rilevatore.ente_appartenenza,
specie.nome_comune,
specie.nome_scientifico
from
evento_investimento
JOIN specie ON evento_investimento.specie_id = specie.specie_id
JOIN rilevatore ON evento_investimento.rilevatore_id = rilevatore.rilevatore_id;
When I attempt to fill the data I receive an error from postgres since view generated from different tables aren't updatable by default.
Thus, I implemetend the following trigger to overcome this issue.
CREATE OR REPLACE FUNCTION inserimento_vista() RETURNS trigger AS $$
BEGIN
INSERT INTO evento_investimento (data,ora)
VALUES (NEW.data,NEW.ora);
INSERT INTO rilevatore (nome_cognome, telefono, email, ente_appartenenza)
VALUES (NEW.nome_cognome, NEW.telefono, NEW.email, NEW.ente_appartenenza);
INSERT INTO specie (nome_comune, nome_scientifico)
VALUES (NEW.nome_comune, NEW.nome_scientifico);
RETURN NEW;
END;
$$ LANGUAGE plpgsql;
create trigger inserimento_vista_trg
instead of insert on investimenti_vista for each row EXECUTE procedure inserimento_vista();
However this is not working due to unique contraints I have in the rilevatore and specie tables. How I can solve this?
Thanks
You might try to check for the existence of the conflicting values like this:
CREATE OR REPLACE FUNCTION inserimento_vista() RETURNS trigger AS $$
BEGIN
INSERT INTO evento_investimento (data,ora)
VALUES (NEW.data,NEW.ora);
if not exists(select * from rilevatore where rilevatore.nome_cognome=new.nome_cognome) then
INSERT INTO rilevatore (nome_cognome, telefono, email, ente_appartenenza)
VALUES (NEW.nome_cognome, NEW.telefono, NEW.email, NEW.ente_appartenenza);
end if;
if not exists(select * from specie where specie.nome_comune=new.nome_comune) then
INSERT INTO specie (nome_comune, nome_scientifico)
VALUES (NEW.nome_comune, NEW.nome_scientifico);
end if;
RETURN NEW;
END;
$$ LANGUAGE plpgsql;
You might want to add to this an update the specie and/or rilevatore tables with the non-conflicting values but that's up to you :-)
Basically, users when they create a new record in mytable1, there is an id field that needs to be the same across multiple tables. I achieve this by having mytable2 with the s_id as primary key
My current function looks like
CREATE OR REPLACE FUNCTION test.new_record()
RETURNS trigger
LANGUAGE plpgsql
AS $function$
BEGIN
case when new.s_id in (select s_id from mytable1) then
insert into mytable2 (sprn, date_created) select max(s_id) +1, now() from mytable2 ;
update mytable1 set new.s_id = (select max(b.s_id) from mytable2 b);
end case;
RETURN new;
END;
$function$;
Intended was when the s_id is replicated then it would create a new entry on mytable2. This new entry would then be updated onto mytable1
Problem with this function is that right now it does not recognise the new on the update part of the function.
How to keep the s_id take the value on every new insert ?
If you want to have one "generator" across multiple tables, create one sequence that is used across all those tables for the default value:
create sequence the_id_sequence;
create table one
(
id integer primary key default nextval('the_id_sequence')
.... other columns
);
create table two
(
id integer primary key default nextval('the_id_sequence')
.... other columns ...
);
If you want to replicate an ID from one table to another during insert, you only need one sequence:
create table one
(
-- using identity is the preferred over "serial" to auto-generate PK values
id integer primary key generated always as identity
);
create table two
(
id integer primary key
);
create or replace function insert_two()
returns trigger
as
$$
begin
insert into two (id) values (new.id);
return new;
end;
$$
language plpgsql;
create trigger replicate_id
before insert on one
for each row
execute procedure insert_two();
Then if you run:
insert into one (id) values (default);
A row with exactly the same id value will be inserted into table two.
If you don't have a generated ID column so far, use the following syntax:
alter table one
add testidcolumn bigint generated always as identity;
I'm trying to update tables from insert or update call on a PostgreSQL view. Here's a simplified example of what I do:
[Person] table:
id | lastname | firstname | city | age
[Person_View] table:
id | lastname | firstname | city
Here is the trigger and the related procedure :
CREATE TRIGGER tg_update_person_view
INSTEAD OF INSERT OR UPDATE OR DELETE ON
Person_View FOR EACH ROW EXECUTE PROCEDURE update_person_view_table();
CREATE OR REPLACE FUNCTION update_person_view_table()
RETURNS TRIGGER
LANGUAGE plpgsql
AS $function$
BEGIN
IF TG_OP = 'INSERT' THEN
INSERT INTO Person (id, lastname, firstname)
VALUES(NEW.id, NEW.lastname, NEW.firstname);
RETURN NEW;
ELSIF TG_OP = 'UPDATE' THEN
UPDATE Person
SET id=NEW.id, lastname=NEW.lastname, firstname=NEW.firstname
WHERE id=OLD.id;
RETURN NEW;
END IF;
RETURN NEW;
END;
$function$;
If I do:
INSERT INTO Person_View (id, city) VALUES ('3', 'Berlin')
A row with only the ID is added to the view and the parent table.
How can I check in the procedure that columns in which values are being inserted have a "mapping" defined in the procedure and if there ain't any mapped columns, it does not proceed ?
You can define a check constraint on the table, e.g.:
create table person(
id int primary key,
lastname text,
firstname text,
city text,
age int,
check(coalesce(lastname, firstname, city, age::text) is not null)
);
insert into person (id)
values (1);
ERROR: new row for relation "person" violates check constraint "person_check"
DETAIL: Failing row contains (1, null, null, null, null).
The solution works regardless whether any views based on the table were created or not.
Have a separate trigger & trigger function for ON DELETE to simplify. (You are not doing anything ON DELETE anyway?)
A CHECK constraint like klin suggested seems like a good idea. You don't need COALESCE and casting, though. Check a row value for NULL.
CHECK (NOT ROW(lastname, firstname) IS NULL) -- ROW keyword is noise
This enforces at least one notnull value in the row. Works for any number of columns and any data type.
Note in particular that ROW(lastname, firstname) IS NOT NULL is not the same and would not work. Detailed explanation:
NOT NULL constraint over a set of columns
If the CHECK constraint is not an option, you can use the same expression in a trigger - which should be faster than adding it to the trigger function. The manual on CREATE TRIGGER:
Also, a trigger definition can specify a Boolean WHEN condition, which
will be tested to see whether the trigger should be fired. In
row-level triggers the WHEN condition can examine the old and/or new
values of columns of the row.
CREATE TRIGGER tg_update_person_view
INSTEAD OF INSERT OR UPDATE ON Person_View
FOR EACH ROW
WHEN (NOT (NEW.lastname, NEW.firstname) IS NULL) -- more columns?
EXECUTE PROCEDURE update_person_view_table();
If the WHEN expression does not evaluate to TRUE, the trigger function is not even called - so it does not proceed like requested.
However, I missed your trigger INSTEAD OF. The manual:
INSTEAD OF triggers do not support WHEN conditions.
In this case you have to move the check into the function body:
IF NOT (NEW.lastname, NEW.firstname) IS NULL THEN
-- do stuff
END IF;
Hi people i need some help deciding on the best way to do an insert into table ‘shop’ which has a serial id field. I also need to insert into tables ‘shopbranch’ and ‘shopproperties’ which both references shop.id.
In a nutshell I need to insert one shop record. Then two records for each table of the following tables, shopproperty and shopbranch, whose shopid (FK) references the just created shop.id field
I saw somewhere that i could wrap the ‘shop’ insert, inside a function called lets say ‘insert_shop’ which does the 'shop' insert and returns its id using a select statement
Then inside another function which inserts shoproperty and shopbranch records i could do one call to insert_shop function to return the shop id which can be used to be passed in as the shop id for the records.
Can you let me know if I’m looking at this in the correct way as I’m a newbie.
One way to approach this is to create a view on your three tables that shows all columns from all three tables that can be inserted or updated. If you then create an INSTEAD OF INSERT trigger on the view then you can manipulate the view contents as if it were a table. You can do the same with UPDATE and even combine the two into an INSTEAD OF INSERT OR UPDATE trigger. The function that your trigger calls then has three INSERT statements that redirect the insert on the view to the underlying tables:
CREATE TABLE shop (
id serial PRIMARY KEY,
nm text,
...
);
CREATE TABLE shopbranch (
id serial PRIMARY KEY,
shop integer NOT NULL REFERENCES shop,
branchcode text,
loc text,
...
);
CREATE TABLE shopproperties (
id serial PRIMARY KEY,
shop integer NOT NULL REFERENCES shop,
prop1 text,
prop2 text,
...
);
CREATE VIEW shopdetails AS
SELECT s.*, b.*, p.*
FROM shop s, shopbranch b, shopproperties p,
WHERE b.shop = s.id AND p.shop = s.id;
CREATE FUNCTION shopdetails_insert() RETURNS trigger AS $$
DECLARE
shopid integer;
BEGIN
INSERT INTO shop (nm, ...) VALUES (NEW.nm, ...) RETURNING id INTO shopid;
IF NOT FOUND
RETURN NULL;
END;
INSERT INTO shopbranch (shop, branchcode, loc, ...) VALUES (shopid, NEW.branchcode, NEW.loc, ...);
INSERT INTO shopproperties(shop, prop1, prop2, ...) VALUES (shopid, NEW.prop1, NEW.prop2, ...);
RETURN NEW;
END; $$ LANGUAGE plpgsql;
CREATE TRIGGER shopdetails_trigger_insert
INSTEAD OF INSERT
FOR EACH ROW EXECUTE PROCEDURE shopdetails_insert();
You could of course play with the view and show only those columns from the three tables that can be inserted or updated (such as excluding primary and foreign keys).