CREATE TABLE book (
book_type char(3),
book_name character varying(100),
book_desc character varying(1000),
PRIMARY KEY (book_type, book_name)
);

CREATE TABLE audience (
aud_type char(3),
aud_name character varying(100),
aud_desc character varying(1000),
PRIMARY KEY (aud_type, aud_name)
);

CREATE TABLE book_audience (
book_type char(3),
book_name character varying(100),
aud_type char(3),
aud_name character varying(100),
PRIMARY KEY (book_type, book_name, aud_type, aud_name),
FOREIGN KEY (book_type, book_name) references book (book_type, book_name),
FOREIGN KEY (aud_type, aud_name) references audience (aud_type, aud_name)
);

SELECT a.a_id, b.b_id, b.b_desc,  
CASE WHEN x.b_id IS NULL THEN 'F' ELSE 'T' END AS selected 
FROM a 
CROSS JOIN b 
LEFT JOIN x ON (x.a_id = a.a_id AND x.b_id = b.b_id) 
WHERE (a.a_id = 'whatever')