数据库关系代数，SQL查询

Question

5.Consider以下库架构

Books (book_no,title,authors,publisher) 
Borrower(borrower_id, name, DOB, job) 
Borrowed(borrower_id,book_no,date) 

写关系代数

• 一个下列查询。查找借用“Wiley”发布的3本以上书籍的借款人的姓名和借阅人ID
• b。查找借用“wiley”
• 发布的任何书的借用人的姓名c。找到每个借款人借入的书籍的平均数量。

Answer 1

按你的问题，SQL查询是这样

问题1

select B.borrower_id, B.name 
    from Borrower as B, Borrowed as Bw, Books as Bk 
where B.borrower_id = Bw.borrower_id 
    and Bw.book_no = Bk.book_no 
    and Bk.publisher = 'Wiley' 
group by B.borrower_id, B.name 
having count(Bw.borrower_id) > 3 

问题2

select B.name 
    from Borrower as B, Borrowed as Bw, Books as Bk 
where B.borrower_id = Bw.borrower_id 
    and Bw.book_no = Bk.book_no 
    and Bk.publisher = 'Wiley' 
    group by B.name 

问题3

select B.borrower_id, B.name, count(Bw.borrower_id) as cnt 
    from Borrower as B, Borrowed as Bw, Books as Bk 
where B.borrower_id = Bw.borrower_id 
    and Bw.book_no = Bk.book_no 
group by B.borrower_id, B.name