如何在一个表中使用另一个表中的FK填充我的FK列？

Question

I have got a football world cup database. These are the two important table I'm working on right now:

CREATE TABLE Countries(
   Cid SERIAL PRIMARY KEY,
   Name VARCHAR(256) NOT NULL UNIQUE
);

CREATE TABLE Clubs(
   Ncid SERIAL PRIMARY KEY,
   Name VARCHAR(256) NOT NULL UNIQUE,
   Cid INT REFERENCES Countries NOT NULL
);

So I added a column 'country' in the clubs table which represents the country the club is in. The problem now is I need to populate the cid column of the clubs table with the cid that matches the country in the countries table.

I have tried this and it didn't work:

ALTER TABLE clubs ADD COLUMN country VARCHAR(255)
INSERT INTO clubs(name, country) 
SELECT DISTINCT club_name, club_country 
FROM tempsquads; //this loads the data from a temporary tabe into my table

INSERT INTO clubs(cid) 
SELECT cid 
FROM countries 
WHERE clubs.country = countries.name;

Has anyone an idea of how I can perform such a query?

Answer 1

In your INSERT, link tempsquads to country:

INSERT INTO CLUBS(name, cid)
(SELECT t.club_name, c.cid
FROM tempsquads t
INNER JOIN COUNTRIES c ON t.club_country=c.name)

Don't add the country name field to the clubs table--you will link on id when you need the name.