图书(图书号,图书名,作者编号,出版社,出版日期) 作者(作者姓名,作者编号,年龄,性别) 用SQL语句查询年龄小于平均年龄的作者姓名、图书名,出版社。
两个表: books, authors
select authors.name, books.title, books.publisher from books inner join authors on books.ID = authors.ID where authors.age < (select avg(age) from authors);