Question

I have these relationships:

User(uid:integer,uname:varchar), key is uid
Recipe(rid:integer,content:text), key is rid
Rating(rid:integer, uid:integer, rating:integer) , key is (uid,rid).

I built the table in the following way:

CREATE TABLE User(
    uid INTEGER PRIMARY KEY ,
    uname VARCHAR NOT NULL
);
CREATE TABLE Recipes(
    rid INTEGER PRIMARY KEY,
    content VARCHAR NOT NULL
);

Now for the Rating table: I want it to be impossible to insert a uid\rid that does not exist in User\Recipe.
My question is: which of the following is the correct way to do it? Or please suggest the correct way if none of them are correct. Moreover, I would really appreciate if someone could explain to me what is the difference between the two.

First:

CREATE TABLE Rating(
    rid INTEGER,
    uid INTEGER,
    rating INTEGER CHECK (0<=rating and rating<=5) NOT NULL,
    PRIMARY KEY(rid,uid),
    FOREIGN KEY (rid) REFERENCES Recipes,
    FOREIGN KEY (uid) REFERENCES User
);

Second:

  CREATE TABLE Rating(
      rid INTEGER REFERENCES Recipes,
      uid INTEGER REFERENCES User,
      rating INTEGER CHECK (0<=rating and rating<=5) NOT NULL,
      PRIMARY KEY(rid,uid)
  );

EDIT:
I think User is problematic as a name for a table so ignore the name.

Answer 1

Technically both versions are the same in Postgres. The docs for CREATE TABLE say so quite clearly:

There are two ways to define constraints: table constraints and column constraints. A column constraint is defined as part of a column definition. A table constraint definition is not tied to a particular column, and it can encompass more than one column. Every column constraint can also be written as a table constraint; a column constraint is only a notational convenience for use when the constraint only affects one column.

So when you have to reference a compound key a table constraint is the only way to go.

But for every other case I prefer the shortest and most concise form where I don’t need to give names to stuff I’m not really interested in. So my version would be like this:

CREATE TABLE usr(
    uid SERIAL PRIMARY KEY ,
    uname TEXT NOT NULL
);
CREATE TABLE recipes(
    rid SERIAL PRIMARY KEY,
    content TEXT NOT NULL
);
CREATE TABLE rating(
    rid INTEGER REFERENCES recipes,
    uid INTEGER REFERENCES usr,
    rating INTEGER NOT NULL CHECK (rating between 0 and 5),
    PRIMARY KEY(rid,uid)
);