PostgreSQL - SUB_QUERY

SUB-QUERY

-- simple sub-query
SELECT title FROM books WHERE author_id=(SELECT id FROM authors WHERE last_name='Geisel' AND first_name='Theodor Seuss');

-- sub-query using IN
SELECT title FROM books WHERE author_id IN (SELECT id FROM authors WHERE last_name ~ '^[A-E]');

-- multi-column sub-query using IN
SELECT isbn, cost, retail FROM stock
    WHERE (isbn, stock)
    IN (SELECT isbn, 0 FROM editions
        WHERE type='p');