問題描述
SELECT MAX(AVG(SYSDATE - inv_date)) FROM invoice;
這個查詢有什么問題?
Avg 返回單個值 否Max 需要一個小組來處理，所以它不會執行并給出錯誤?請解釋工作這是一個不會執行的測驗問題 我想知道它不執行的原因 我不知道允許嵌套聚合函數嗎?
Avg returns single value no Max requires a group to work on so it dosent execute and give error? Please explain working It's a quiz question according to which it won't execute I want to know the reason why it dosent execute I can't figure it out nested aggregate functions are allowed right?
推薦答案
Oracle 允許嵌套聚合函數(參見 文檔).
Oracle allows nested aggregation functions (see the documentation).
然而，它需要一個GROUP BY.所以這是允許的:
However, it requires a GROUP BY. So this is allowed:
SELECT MAX(AVG(SYSDATE - inv_date))
FROM invoice
GROUP BY Cust_ID;
基本上，這是一個捷徑:
Basically, this is a short-cut for:
SELECT MAX(x)
FROM (SELECT AVG(SYSDATE - inv_date) as x
FROM invoice
GROUP BY Cust_Id
) i;
不過，就您而言，沒有 GROUP BY.Oracle 不允許在沒有 GROUP BY 的情況下嵌套 GROUP BY.
In your case, though, there is no GROUP BY. Oracle doesn't allow nested GROUP BY without the GROUP BY.
如果您好奇，我不喜歡這種擴展功能.我不認為它實際上解決了問題.
And if you are curious, I'm not a fan of this extended functionality. I don't see that it actually solves a problem.
這篇關于嵌套聚合函數的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！