如何避免在oracle中重複？

Question

SELECT title, retail, (SELECT AVG(retail) 
       FROM books) 
FROM books 
WHERE retail < (SELECT AVG(retail) 
       FROM books) 

有沒有辦法將（選擇AVG（零售） 從書籍中的一個）縮短爲別名？

Answer 1

試試這個：

SELECT * 
    FROM (
    SELECT title, retail, AVG(retail) OVER() avg_retail 
    FROM books 
    ) 
WHERE retail < avg_retail 

，或者使用WITH：

WITH dat AS 
(
    SELECT title, retail, AVG(retail) OVER() avg_retail 
    FROM books 
) 
SELECT * 
    FROM dat 
WHERE retail < avg_retail 

Answer 2

，你可以用WITH條款重構，也許是這樣的：

With avg_retail as 
    (SELECT AVG(retail) the_avg 
    FROM books) 
SELECT title, retail, avg_retail.the_avg 
from books, avg_retail 
where books.retail < avg_retail.the_avg;