SQL多表查詢

Question

嗨，有人可以幫我解決這個問題。我花了年齡試圖找出什麼我做錯了，但沒有運氣

表

1. 出版商（PUBLISHERNAME，位置，noOftitles）
2. 作者（名稱，位置）
3. 書（書名，ISBN，成本，AUTHORNAME，PUBLISHERNAME）

問題

編寫一條SQL命令，以針對具有多個作者的每個發佈者，發佈者的名稱，發佈者的位置以及發佈者銷售的圖書的平均成本顯示。

代碼：

SELECT Book.publishername, location, avg(cost) 
FROM Publisher 
,  Book 
WHERE Publisher.publisherName = Book.publisherName 
GROUP 
BY  publisherName 
HAVING COUNT (DISTINCT authorname) >1 

錯誤

ORA-00918：列定義的含糊

正確答案：

SELECT Publisher.publisherName, Publisher.location, avg(cost) 
FROM Publisher, Book 
WHERE Publisher.publisherName = Book.publisherName 
GROUP BY Publisher.PublisherName, Publisher.Location 
HAVING COUNT (DISTINCT authorname) >1; 

Answer 1

您的選擇中有不明確的列名。 select語句中的location可能來自Publisher表或Author表，並且GROUP BY中的publisherName可能來自Publisher或Book。您需要明確指定要從哪些表中獲取這些值。

SELECT Book.publishername, Publisher.location, avg(cost) 
FROM Publisher, Book 
WHERE Publisher.publisherName =Book.publisherName 
GROUP BY publisher.publisherName 
HAVING COUNT (DISTINCT authorname) >1; 

編輯：關於你的評論，你有你的選擇列，要麼是沒有在GROUP BY或一個非集合函數（如SUM，AVG等）。您需要包括location在GROUP BY：

SELECT Book.publishername, Publisher.location, avg(cost) 
FROM Publisher, Book 
WHERE Publisher.publisherName =Book.publisherName 
GROUP BY publisher.publisherName, Publisher.location 
HAVING COUNT (DISTINCT authorname) >1; 

Answer 2

它不應該是GROUP BY Book.publisherName？

Answer 3

位置在兩個表中。您可以通過使用TABLE.COLUMN來定義它：

Publisher.location 

Answer 4

你GROUP BY應該讀 GROUP BY Book.publishername

Answer 5

答案並解釋是怎麼回事。以下是您的查詢：

SELECT Book.publishername, location, avg(cost) 
FROM Publisher, Book 
WHERE Publisher.publisherName =Book.publisherName 
GROUP BY publisherName 
---------^ 
HAVING COUNT (DISTINCT authorname) >1; 

Oracle不知道列的來源。它可以來自任何一個表格。所以，用表別名前綴所有列。此外，請使用正確的連接語法，而不是隱式連接。這裏是你的查詢的更好的版本：

SELECT b.publishername, p.location, avg(b.cost) 
FROM Publisher p join 
    Book b 
    on p.publisherName = b.publisherName 
GROUP BY b.publisherName 
HAVING COUNT(DISTINCT b.authorname) > 1; 

我想在表的列從哪裏來。