I have to create an api with a database that I will implement later using node.js
I have this one problem though :
I want my foreign key to hold multiple id's because a product can have multiple region. Is there any way I can do it ? I am using postgreSQL
CREATE TABLE product(
id SERIAL PRIMARY KEY,
productName VARCHAR(128),
productCode VARCHAR(10)
);
CREATE TABLE region(
id SERIAL PRIMARY KEY,
regionName VARCHAR(128)
);
ALTER TABLE product ADD COLUMN idRegion INT;
ALTER TABLE product ADD CONSTRAINT idRegion FOREIGN KEY (idRegion) REFERENCES region(id);
INSERT INTO region (id, regionname) VALUES
(1, 'US'),
(2, 'EUR'),
(3, 'AEJ'),
(4, 'JPY'),
(5, 'EM'),
(6, 'CAD'),
(7, 'Brazil and LatAM');
INSERT INTO product (productName, productcode, idRegion) VALUES
('Index Option', 'IO', (1,2,3,4,5,6,7));
I created a third table thank you guys for your answers
CREATE TABLE productRegion(
idRegion INT,
idProduct INT
);
ALTER TABLE productRegion ADD CONSTRAINT idRegion FOREIGN KEY (idRegion) REFERENCES region(id);
ALTER TABLE productRegion ADD CONSTRAINT idProduct FOREIGN KEY (idProduct) REFERENCES product(id);
ALTER TABLE productRegion ADD PRIMARY KEY (idRegion, idProduct);
Related
I have created the tables with following code, but the foreign key constraints does not allow data addition. What can I do to solve this problem?
CREATE TABLE Employee(
Ssn VARCHAR(10) PRIMARY KEY NOT NULL,
BDate DATE,
FName VARCHAR(25),
MInit VARCHAR(5),
LName VARCHAR(25),
Address VARCHAR(40),
Sex VARCHAR(6),
Salary INT,
SupervisorSsn VARCHAR(10),
DNumber INT
);
CREATE TABLE
CREATE TABLE Department(
DNumber INT PRIMARY KEY NOT NULL,
DName VARCHAR(15),
MgrSsn VARCHAR(10),
MgrStartDate DATE,
NumberofEmployees INT,
CONSTRAINT Department_MgrSsn_FK FOREIGN KEY(MgrSsn) REFERENCES Employee(Ssn) ON DELETE SET DEFAULT ON UPDATE CASCADE
);
ALTER TABLE Employee
ADD CONSTRAINT Employee_SupervisorSsn_FK FOREIGN KEY(SupervisorSsn) REFERENCES Employee(Ssn) ON DELETE SET DEFAULT ON UPDATE CASCADE,
ADD CONSTRAINT Employee_DNumber_FK FOREIGN KEY(DNumber) REFERENCES Department(DNumber) ON DELETE SET DEFAULT ON UPDATE CASCADE;
There are several ways to do that in Postgres.
Update later
The most obvious one: insert null values firs, then update it later:
insert into department
(dnumber, dname)
values
(1, 'One'),
(2, 'Two'),
(3, 'Three');
insert into employee (ssn, fname, lname, supervisorssn, dnumber)
values
('123', 'Arthur', 'Dent', '456', 1),
('456', 'Ford', 'Prefect', null, 2),
('789', 'Zaphod', 'Beeblebrox', null, 3);
update department
set mgrssn = '456'
where dnumber in (1,2);
update department
set mgrssn = '789'
where dnumber = 3;
Online example
Deferred constraints
Make the constraints deferred, so that they will be checked at the end of the transaction, rather when running the INSERT:
ALTER TABLE department
add constraint fk_dempt2emp foreign key (mgrssn) references employee
deferrable initially deferred; --<<
Then you can insert the rows in any order you like as long as everything happens in a single transaction:
begin transaction; --<< important!
insert into department
(dnumber, dname, mgrssn)
values
(1, 'One', '456'),
(2, 'Two', '456'),
(3, 'Three', '789')
insert into employee (ssn, fname, lname, supervisorssn, dnumber)
values
('123', 'Arthur', 'Dent', '456', 1),
('456', 'Ford', 'Prefect', null, 2),
('789', 'Zaphod', 'Beeblebrox', null, 3);
commit; -- the FKs will be checked here
Do everything in a single statement
You can use a data modifying CTE to insert rows into two tables. As this is evaluated as a single statement, the constraints do not need to be deferrable.
with new_depts as (
insert into department
(dnumber, dname, mgrssn)
values
(1, 'One', '456'),
(2, 'Two', '456'),
(3, 'Three', '789')
)
insert into employee (ssn, fname, lname, supervisorssn, dnumber)
values
('123', 'Arthur', 'Dent', '456', 1),
('456', 'Ford', 'Prefect', null, 2),
('789', 'Zaphod', 'Beeblebrox', null, 3)
;
Online example
I try to create code for postgresql
CREATE TABLE kaart (
kaartid integer NOT NULL,
naam character varying,
saldo real,
kaarthouderid integer
);
CREATE TABLE kaart_product (
kaartkaartid integer,
productid2 integer
);
CREATE TABLE kaarthouder (
id integer NOT NULL,
naam character varying(255),
naw character varying(255),
geslacht "char"
);
CREATE TABLE product (
naam character varying,
id integer NOT NULL
);
ALTER TABLE ONLY kaart
ADD CONSTRAINT kaart_pkey PRIMARY KEY (kaartid);
ALTER TABLE ONLY kaarthouder
ADD CONSTRAINT kaarthouder_pkey PRIMARY KEY (id);
ALTER TABLE ONLY product
ADD CONSTRAINT product_pkey PRIMARY KEY (id);
ALTER TABLE ONLY kaart
ADD CONSTRAINT kaartco FOREIGN KEY (kaartid) REFERENCES kaarthouder(id) ON UPDATE CASCADE ON DELETE CASCADE;
ALTER TABLE ONLY kaart_product
ADD CONSTRAINT kaartkaartidco FOREIGN KEY (kaartkaartid) REFERENCES kaart(kaartid) ON UPDATE CASCADE ON DELETE CASCADE;
ALTER TABLE ONLY kaart_product
ADD CONSTRAINT productidco FOREIGN KEY (kaartkaartid) REFERENCES product(id) ON UPDATE CASCADE ON DELETE CASCADE;
INSERT INTO kaart VALUES (1, 'Sander',50.00 ,1);
INSERT INTO kaart_product VALUES (1,1);
INSERT INTO kaarthouder VALUES (1, 'Sander','test,testing','man');
INSERT INTO product VALUES ('studentenproduct',1);
But whenever i try to run it it gives me this error:
23503: insert or update on table "kaart" violates foreign key constraint "kaartco"
But i really dont know why this happens since it is the same to the other foreign keys that are below it
So can someone help me fix this?
You try to link to a product and a kaart that doesn't exist yet.
Move:
INSERT INTO kaart_product VALUES (1,1);
Two lines down under:
INSERT INTO product VALUES ('studentenproduct',1);
That should do the job for you.
Try to search google for forgein key contstraints and how they work.
I have table tariffs, with two columns: (tariff_id, reception)
I have table users, with two columns: (user_id, reception)
And I have table users_tariffs with two columns: (user_id, tariff_id).
I want to prevent situation when tariff from one reception is assigned to user from another reception. How can I do that?
E.G
Users:
user_id | reception
Putin | Russia
Trump | USA
Tariffs:
tariff_id | reception
cheap | USA
expensive | Russia
Wrong situation at users_tariffs, because Cheap tariff is for USA only:
user_id | tariff_id
Putin | Cheap
SOLUTION 1: FOREIGN KEY CONSTRAINTS
I am assuming the following table definitions.
In particular, the composite key in user_tariffs makes this a many-to-many relationship between users and tariffs.
CREATE TABLE tariffs (tariff_id int NOT NULL PRIMARY KEY,
reception text NOT NULL);
CREATE TABLE users (user_id int NOT NULL PRIMARY KEY,
reception text NOT NULL);
CREATE TABLE user_tariffs (tariff_id int NOT NULL REFERENCES tariffs (tariff_id),
user_id int NOT NULL REFERENCES users (user_id),
PRIMARY KEY (tariff_id, user_id));
You probably need a combination of all three columns somewhere, so let's create this:
ALTER TABLE user_tariffs ADD COLUMN reception text;
UPDATE user_tariffs a
SET reception = b.reception
FROM (SELECT * FROM tariffs) b
WHERE a.tariff_id = b.tariff_id;
ALTER TABLE user_tariffs ALTER COLUMN reception SET NOT NULL;
Now we can use FOREIGN KEY REFERENCES (user_id, reception) into users.
CREATE UNIQUE INDEX ON tariffs (tariff_id, reception);
ALTER TABLE user_tariffs ADD FOREIGN KEY (tariff_id, reception)
REFERENCES tariffs (tariff_id, reception);
In addition, we can use FK REFs (tariff_id, reception) into tariffs.
CREATE UNIQUE INDEX ON users (user_id, reception);
ALTER TABLE user_tariffs ADD FOREIGN KEY (user_id, reception)
REFERENCES users (user_id, reception);
Populate with data:
INSERT INTO users VALUES (1, 'cheap'), (2, 'expensive');
INSERT INTO tariffs VALUES (1, 'cheap'), (2, 'expensive');
Now assume we have the following data (user_id, tariff_id) to insert:
WITH data (user_id, tariff_id)
AS (VALUES (1, 2), (2, 1)), -- here is your application data
datas (user_id, tariff_id, reception)
AS (SELECT user_id,
tariff_id,
(SELECT u.reception -- reception calculated by user
FROM users u
WHERE u.user_id = d.user_id)
FROM data d)
INSERT INTO user_tariffs SELECT * FROM datas ;
Then you cannot insert the data, because you can only add (1, 1) or (2, 2) with the same reception, but not (1, 2) or (2, 1) with different reception's. The error message is:
ERROR: insert or update on table "user_tariffs" violates foreign key constraint "user_tariffs_user_id_fkey1"
DETAIL: Key (user_id, reception)=(2, cheap) is not present in table "users".
But you can insert with data AS VALUES (1, 1), (2, 2).
I think the FOREIGN KEY CONSTRAINT solution is to be preferred.
Please describe your functional dependencies, if you want better table designs.
SOLUTION 2: TRIGGER
-- DROP TABLE user_tariffs CASCADE;
-- DROP TABLE users CASCADE;
-- DROP TABLE tariffs CASCADE;
CREATE TABLE tariffs (tariff_id int NOT NULL PRIMARY KEY,
reception text NOT NULL);
CREATE TABLE users (user_id int NOT NULL PRIMARY KEY,
reception text NOT NULL);
CREATE TABLE user_tariffs (tariff_id int NOT NULL REFERENCES tariffs (tariff_id),
user_id int NOT NULL REFERENCES users (user_id),
PRIMARY KEY (tariff_id, user_id));
INSERT INTO users VALUES (1, 'cheap'), (2, 'expensive');
INSERT INTO tariffs VALUES (1, 'cheap'), (2, 'expensive');
-- table user_tariffs (user_id, tariff_id) only, without reception column.
Create a function with return type trigger:
CREATE OR REPLACE FUNCTION check_reception()
RETURNS trigger AS $$
DECLARE valid boolean := false;
BEGIN
SELECT (SELECT u.reception FROM users u WHERE u.user_id = NEW.user_id)
= (SELECT t.reception FROM tariffs t WHERE t.tariff_id = NEW.tariff_id)
INTO valid FROM user_tariffs ;
IF valid = false
THEN RAISE EXCEPTION '(user, tariff, reception) invalid.';
END IF;
RETURN NEW;
END; $$ LANGUAGE plpgsql ;
and register it:
CREATE TRIGGER reception_trigger
AFTER INSERT OR UPDATE ON user_tariffs
FOR EACH ROW EXECUTE PROCEDURE check_reception();
Now try to insert (1, 2), which would be (cheap, expensive) and is not allowed:
INSERT INTO user_tariffs VALUES (1, 2);
ERROR: (user, tariff, reception) invalid.
KONTEXT: PL/pgSQL function check_reception() line 7 at RAISE
But we can insert (1, 1), which is (cheap, cheap) without problem:
INSERT INTO user_tariffs VALUES (1, 1);
SELECT * FROM user_tariffs;
Remark
Triggers are not the best solution here, in my opinion. Try to avoid triggers, if possible. They can have side effects (transactions etc). Check StackOverflow for further details :)
Is it possible to assign a foreign key to a json property in PostgreSQL? Here is an example what I would like to achieve, but it doesn't work:
CREATE TABLE Users (Id int NOT NULL PRIMARY KEY);
CREATE TABLE Data (
Id int NOT NULL PRIMARY KEY,
JsonData json NOT NULL, -- [{Id: 1, somedata: null},{Id: 2, somedata: null}, ...]
CONSTRAINT FK_Users_Data FOREIGN KEY (JsonData->Id) REFERENCES Users(Id) -- this constraint will fail
);
It is not possible, and may not ever be possible, to assign a foreign key to a json property. It'd be a major and quite complicated change to PostgreSQL's foreign key enforcement. I don't think it's impossible to do, but would face similar issues to those experienced by the foreign-keys-to-arrays patch.
With 9.4 it'll be possible to make a whole json object a foreign key as jsonb supports equality tests. In 9.3 you can't even do that.
Here's a little SPI function have_ids which I use for an integrity constraint on a one-to-many relationship with a jsonb column
CREATE TABLE foo (
id INTEGER NOT NULL
)
CREATE TABLE bar (
foo_ids pg_catalog.jsonb DEFAULT '[]'::jsonb NOT NULL,
CONSTRAINT bar_fooids_chk CHECK (have_ids ('foo', foo_ids))
)
With a couple of triggers on foo it's almost as good as a foreign key.
The foreign key parameter must be a column name:
http://www.postgresql.org/docs/current/static/sql-createtable.html
You will have to normalize
create table user_data (
id int not null primary key,
user_id int not null,
somedata text,
constraint fk_users_data foreign key (user_id) references Users(Id)
);
Yes it is possible but you will have to store another value. If you change your schema to:
CREATE TABLE Users (Id int NOT NULL PRIMARY KEY);
CREATE TABLE Data (
Id int NOT NULL PRIMARY KEY,
JsonData json NOT NULL,
UserId int generated always as ((JsonData->>'Id')::int) stored references Users(Id)
);
INSERT INTO Users VALUES (1);
Foreign key that doesn't exist:
INSERT INTO Data VALUES (1, '{"Id": 3}');
Returns the error:
ERROR: insert or update on table "data" violates foreign key constraint "data_userid_fkey" DETAIL: Key (userid)=(3) is not present in table "users".
Foreign key that does work:
INSERT INTO Data VALUES (1, '{"Id": 1}');
I am struggling with foreign keys in my DB, possibly it has something to do with inheritance?
So here's the basic setup:
-- table address
CREATE TABLE address
(
pk_address serial NOT NULL,
fk_gadmid_0 integer NOT NULL, -- this table already exists, no problem here
street character varying(100),
zip character varying(10),
city character varying(50),
public boolean,
CONSTRAINT address_primarykey PRIMARY KEY (pk_address),
CONSTRAINT gadmid_0_primarykey FOREIGN KEY (fk_gadmid_0)
REFERENCES adm0 (gadmid_0) MATCH SIMPLE
ON UPDATE CASCADE ON DELETE NO ACTION
)
WITH (
OIDS=FALSE
);
ALTER TABLE address OWNER TO postgres;
-- table stakeholder (parent)
CREATE TABLE stakeholder
(
pk_stakeholder integer DEFAULT nextval('common_stakeholder_seq') NOT NULL,
fk_stakeholder_type integer NOT NULL, -- this table also exists, no problem here
name character varying(255) NOT NULL,
CONSTRAINT stakeholder_primarykey PRIMARY KEY (pk_stakeholder),
CONSTRAINT stakeholder_fk_stakeholder_type FOREIGN KEY (fk_stakeholder_type)
REFERENCES stakeholder_type (pk_stakeholder_type) MATCH SIMPLE
ON UPDATE CASCADE ON DELETE NO ACTION
)
WITH (
OIDS=FALSE
);
ALTER TABLE stakeholder OWNER TO postgres;
-- table individual (child of stakeholder)
CREATE TABLE individual
(
firstname character varying(50),
fk_title integer, -- this table also exists, no problem here
email1 character varying (100),
email2 character varying (100),
phone1 character varying (50),
phone2 character varying (50),
CONSTRAINT individual_primarykey PRIMARY KEY (pk_stakeholder),
CONSTRAINT title_foreignkey FOREIGN KEY (fk_title)
REFERENCES title (pk_title) MATCH SIMPLE
ON UPDATE CASCADE ON DELETE CASCADE
) INHERITS (stakeholder)
WITH (
OIDS=FALSE
);
ALTER TABLE individual OWNER TO postgres;
-- link between stakeholder and address
CREATE TABLE l_stakeholder_address
(
pk_l_stakeholder_address serial NOT NULL,
fk_stakeholder integer NOT NULL REFERENCES stakeholder,
fk_address integer NOT NULL REFERENCES address,
CONSTRAINT l_stakeholder_address_primarykey PRIMARY KEY (pk_l_stakeholder_address),
CONSTRAINT l_stakeholder_address_fk_stakeholder FOREIGN KEY (fk_stakeholder)
REFERENCES stakeholder (pk_stakeholder) MATCH SIMPLE
ON UPDATE CASCADE ON DELETE NO ACTION,
CONSTRAINT l_stakeholder_address_fk_address FOREIGN KEY (fk_address)
REFERENCES address (pk_address) MATCH SIMPLE
ON UPDATE CASCADE ON DELETE NO ACTION
)
WITH (
OIDS=FALSE
);
ALTER TABLE l_stakeholder_address OWNER TO postgres;
So far, no problem. Then I tried to add some values:
INSERT INTO individual (pk_stakeholder, fk_stakeholder_type, name, firstname, fk_title, email1, email2, phone1, phone2)
VALUES (1, 8, 'Lastname', 'Firstname', 1, 'me#you.com', '', '', '');
INSERT INTO address (pk_address, fk_gadmid_0, street, zip, city, public)
VALUES (1, 126, 'Address', '', 'City', FALSE);
INSERT INTO l_stakeholder_address (pk_l_stakeholder_address, fk_stakeholder, fk_address)
VALUES (DEFAULT, 1, 1);
And finally I end up having an error (SQL state 23503) saying that the key (fk_stakeholder)=(1) is not existing in table "stakeholder".
The first 2 inserts are fine, I can see them in the databases:
stakeholder:
pk_stakeholder | ...
----------------------
1 | ...
address:
pk_address | ...
--------------------
1 | ...
What am I doing wrong? I must admit that I am rather new to PostgreSQL (using 8.4) but I'm not even sure if that is an issue of PG at all, maybe I'm just lacking some basic database design understandings ...
Either way, by now I tried pretty much everything I could think of, I also tried to make the FK deferrable as in PostgreSQL : Transaction and foreign key problem but somehow that doesn't work either.
You can work around it using additional table individual_pks (individual_pk integer primary key) with all primary keys from both parent and child, which will be maintained using triggers (very simple — insert to individual_pks on insert, delete from it on delete, update it on update, if it changes individual_pk).
Then you point foreign keys to this additional table instead of a child. There'll be some small performance hit, but only when adding/deleting rows.
Or forget inheritance and do it the old way - simply one table with some nullable columns.
Your analysis is exactly right: It's because of the inheritance. When checking the foreign key, child tables are not considered.
In general, inheritance and foreign keys don't mix well in PostgreSQL. A major problem is that you can't have unique constraints across tables.
Reference