數據庫關係代數，SQL查詢

Question

5.Consider以下庫架構

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

寫關係代數

• 一個下列查詢。查找借用「Wiley」發佈的3本以上書籍的借款人的姓名和借閱人ID
• b。查找借用「wiley」
• 發佈的任何書的借用人的姓名c。找到每個借款人借入的書籍的平均數量。

Answer 1

按你的問題，SQL查詢是這樣

問題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 

問題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 

問題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