CREATE TABLE ampref (
    ampref_id serial NOT NULL,
    amp_id integer NOT NULL,
    code character varying(255) NOT NULL,   
    description text    
);
CREATE TABLE amp (
    amp_id serial NOT NULL,
    name character varying(255) NOT NULL,
    description character varying(255),    
    url character varying(255)
);

SELECT url FROM amp WHERE name='LUNA';

 
SELECT ar.url
FROM amp a
JOIN ampref ar ON a.amp_id = ar.amp_id
WHERE a.name LIKE 'luna'