select l.bookId,l.ISBN,b.bookName,b.publisher,b.price,l.Ltime
form lend as l,Book as b
where l.readerId=20 and b.ISBN=l.ISBN
------解决思路----------------------
select l.bookId,l.ISBN,b.bookName,b.publisher,b.price,l.Ltime
form lend as l,Book as b
where l.readerId=20 and b.ISBN=l.ISBN
-- from 你拼写错了, 你写成了 form 了。
-- 如下是对的。
select l.bookId,l.ISBN,b.bookName,b.publisher,b.price,l.Ltime
from lend as l,Book as b
where l.readerId=20 and b.ISBN=l.ISBN