column “parent_id” referenced in foreign key constraint does not exist when creating SQL table

I am new in SQL and trying to understand Foreign key syntax. I know this was asked in multiple questions but each question I found did not seem to teach me what I am doing wrong here. This is my SQL code:

CREATE TABLE Customer
(
id int primary key,
name varchar(30),
age int,
gender bool
);

CREATE TABLE Minor
(
FOREIGN KEY (parent_id) REFERENCES Customer(id)
);

CREATE TABLE Adult
(
FOREIGN KEY (parent_id) REFERENCES Customer(id)
);

CREATE TABLE Shop
(
id int primary key
);

CREATE TABLE Drink
(
name varchar(30) primary key
);

CREATE TABLE AlcoholicDrink
(
FOREIGN KEY (name) REFERENCES Drink(name)
);

CREATE TABLE NonAlcoholicDrink
(
FOREIGN KEY (name) REFERENCES Drink(name)
);

And this is the error I am getting:

ERROR:  column "parent_id" referenced in foreign key constraint does not exist
SQL state: 42703

Answer

You need to add fields in your tables to make the reference. Something like this :

CREATE TABLE Customer
(
id int primary key,
name varchar(30),
age int,
gender bool
);

CREATE TABLE Minor
(
minor_id serial primary key,
parent_id int,
other_fields text etc.
FOREIGN KEY (parent_id) REFERENCES Customer(id)
);

This is simply the reason why it’s not working.