如何从同一张表中获取基于实例的结果集？

Question

I have a database with the table "Characters" and the table "Planets" from the star wars movies. I need to find out the names of the characters that have the same affiliation as their homeplanet. The data is in the following images :

Characters

Planets

I tried this but it doesn't work

SELECT character_name
FROM characters c1
INNER JOIN characters c2
ON c1.affiliation = c2.affiliation AND c1.homeworld = c2.homeworld
GROUP BY character_name;

Answer 1

You need to join characters table to planets table by planet name, then filter rows using same affiliations:

SELECT character_name
FROM characters INNER JOIN planets ON characters.homeworld = planets.planet_name
WHERE characters.affiliation = planets.affiliation;

Answer 2

You need to join the two tables and then constrain by the affiliation. You can add this constraint in the join clause or the where clause, so both of these work:

SELECT character_name
FROM characters c
INNER JOIN planets p ON 
  c.homeworld = p.homeworld
  AND c.affiliation = p.affiliation 

or

SELECT character_name
FROM characters c
INNER JOIN planets p ON 
  c.homeworld = p.homeworld
WHERE c.affiliation = p.affiliation