I created this first table named 'bookstore' where Primary Key is book_name:
create table bookstore (book_name varchar primary key, author varchar, price decimal);
I am trying to create a second table named 'name' where name is primary key. I want to make this primary key- author.name as a foreign key of bookstore.author.
create table author (name varchar primary key, place varchar,
constraint fk_author_bookstore foreign key(name) references bookstore(author));
But the error is: ERROR: there is no unique constraint matching given keys for referenced table "bookstore"
SQL state: 42830
I am new to SQL, so, hoping to get some help. If you can, please write the correct code.
Thanks
Name column in author table is primary key and it's referenced as foreign key in bookstore table.
-- PostgreSQL (v11)
create table author (name varchar primary key, place varchar);
create table bookstore (book_name varchar primary key, author varchar, price decimal
, CONSTRAINT fk_author_bookstore
FOREIGN KEY(author)
REFERENCES author(name));
Please check from url https://dbfiddle.uk/?rdbms=postgres_11&fiddle=8394f796433ed8bc170c2889286b3fc2
Add foreign key after table creation
-- PostgreSQL(v11)
ALTER TABLE bookstore
ADD CONSTRAINT fk_author_bookstore FOREIGN KEY (author)
REFERENCES author (name);
Please check from url https://dbfiddle.uk/?rdbms=postgres_11&fiddle=d93cf071bfd0e3940dfd256861be813c
Related
I'm trying to define more than one foreign key in the process table. but I am getting the error that the columns I am trying to define as foreign key are not 'unique value'.
For this, I wanted to define id and name columns as primary keys in category and subject tables. However, when I want to create the process table, I still get this error." there is no unique constraint matching given keys for referenced table "category"
I have researched and continue to do so on Stackoverflow and many more. but I couldn't figure it out with solutions or viewpoints of the issues that got the same error I was facing. Maybe there is something I'm not seeing.
first table;
CREATE TABLE category(
category_id INT GENERATED ALWAYS AS IDENTITY,
category_name VARCHAR(210),
category_description TEXT,
CONSTRAINT category_pk PRIMARY KEY(category_id,category_name)
);
second table;
CREATE TABLE subject(
subject_id INT GENERATED ALWAYS AS IDENTITY,
subject_name VARCHAR(210),
subject_description TEXT,
CONSTRAINT subject_pk PRIMARY KEY(subject_id,subject_name)
);
I tried that too but I keep getting the same error
ALTER TABLE category ADD CONSTRAINT some_constraint PRIMARY KEY(category_id,category_name);
third table;
CREATE TABLE process(
process_id INT GENERATED ALWAYS AS IDENTITY,
fk_category_id INTEGER,
fk_subject_id INTEGER,
FOREIGN KEY(fk_category_id) REFERENCES category(category_id) ON DELETE CASCADE ON UPDATE
CASCADE,
FOREIGN KEY(fk_subject_id) REFERENCES subject(subject_id) ON DELETE CASCADE ON UPDATE
CASCADE
);
In your FOREIGN KEY declaration either:
Include both the columns that make up the PRIMARY KEY on category and subject e.g. ... REFERENCES category(category_id, category_name) ...
OR
Do not refer to any column and let the FK pick up the PK automatically e.g. ... REFERENCES category ON DELETE ....
I am going to say that what you are really after is:
CREATE TABLE category(
category_id INT GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
category_name VARCHAR(210) UNIQUE,
category_description TEXT
);
CREATE TABLE subject(
subject_id INT GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
subject_name VARCHAR(210) UNIQUE,
subject_description TEXT
);
CREATE TABLE process(
process_id INT GENERATED ALWAYS AS IDENTITY,
fk_category_id INTEGER,
fk_subject_id INTEGER,
FOREIGN KEY(fk_category_id) REFERENCES category ON DELETE CASCADE ON UPDATE
CASCADE,
FOREIGN KEY(fk_subject_id) REFERENCES subject ON DELETE CASCADE ON UPDATE
CASCADE
);
An identity column isn't automatically a primary key. So your tables category and subjectdon't have any primary keys and thus can't be referenced by a foreign key.
You need to add PRIMARY KEY to the columns of the tables category and subject
I have two tables, experiment and sample. Samples must be unique within experiments of the same type, but can be shared between experiments that have a different type. I understand how I can add a unique constraint to the samples to make them always unique, but is it possible to create a unique constraint based on the information in the foreign table?
create table experiment (
id integer primary key,
name text,
type text
);
create table sample (
id integer primary key,
name text,
experiment_id integer,
);
alter table sample add constraint exp_fkey foreign key (experiment_id) references experiment(id);
You can create a (redundant) unique constraint on experiment (id, type), add type to sample, create a foreign key constraint from (experiment_id, type) to (id, type) and a unique constraint on sample.type.
I want to create a foreign key in my postgresql db table but i'm receiving still message about non existing table (???!!?) It's driving me crazy because I have created necessary relation (address).
CREATE TABLE base_schema.station
(
id SERIAL PRIMARY KEY NOT NULL,
phone VARCHAR(20) NOT NULL,
station_address INT NOT NULL,
CONSTRAINT station_address_id_fk FOREIGN KEY (station_address)
REFERENCES address (id)
);
CREATE UNIQUE INDEX station_id_uindex ON base_schema.station (id);
I'm using jetbrains datagrip
Thanks in advance
I have a foreign table, for example:
CREATE FOREIGN TABLE film (
id varchar(40) NOT NULL,
title varchar(40) NOT NULL,
did integer NOT NULL,
date_prod date,
kind varchar(10),
len interval hour to minute
)
SERVER film_server;
with id as the primary key for that table (set in the remote database). I would like to have a local table reference the foreign table, and set a foreign key constraint on the local table -- for example:
CREATE TABLE actor (
id varchar(40) NOT NULL,
name varchar(40) NOT NULL,
film_id varchar(40) NOT NULL,
)
ALTER TABLE actor ADD CONSTRAINT actor_film_fkey FOREIGN KEY (film_id)
REFERENCES film(id);
However, when I try to add the foreign key constraint, I get the error:
ERROR: referenced relation "film" is not a table
Is it possible to add a foreign key constraint to a foreign table?
It's no possible create index on foreign tables.
CREATE INDEX idx_film ON film (id);
This is the error:
ERROR: cannot create index on foreign table
Example schema: http://sqlfiddle.com/#!1/3d410
I've already got a table and I want to add a new, not valid foreign key to the table. What's the correct syntax for adding a NOT VALID foreign key?
CREATE TABLE junks (
id serial PRIMARY KEY,
name text
);
CREATE TABLE trunks (
id serial PRIMARY KEY,
name text
-- no fk
);
-- and the below does not work!
--ALTER TABLE trunks ADD junk serial REFERENCES junks(id) NOT VALID;
You first add the column:
alter table trunks add column junk serial;
Then add the constraint to the table:
alter table trunks add constraint the_constraint_name
FOREIGN KEY (junk)
REFERENCES junks (id)
not valid;
This works:
ALTER TABLE trunks ADD CONSTRAINT FK_junk_id
FOREIGN KEY (id)
REFERENCES junks(id)
NOT VALID
;
See, e.g.: http://www.postgresql.org/docs/devel/static/ddl-alter.html#AEN2758