rel-ops.txt

ssd7卡耐基教程

(
	select Book.title, Book.price
	from   Book, PUBLISHER
	where  Book.PublisherID = PUBLISHER.PublisherID and PUBLISHER.PublisherName = '陕西第一出版社'
)
union
(
	select Book.title, Book.price
	from   Book, PUBLISHER
	where  Book.PublisherID = PUBLISHER.PublisherID and PUBLISHER.PublisherName = '陕西第二出版社'
);

used select adn join operations.
In order to search books published by 陕西第一出版社 and 陕西第二出版社, then print them in title and price.
Union operation can join this two select together.