在子查询中使用别名

发布于 2024-10-31 07:32:50 字数 410 浏览 0 评论 0原文

我的一个 SQL 请求出现问题，该请求是通过子查询发出的。

我正在尝试划分两个 COUNT(*) 请求的结果：（

SELECT (SELECT COUNT(*) FROM book) nb_books,
       (SELECT COUNT(*) FROM author) nb_authors,
       nb_books / nb_authors

我的请求要复杂得多，我在示例中对其进行了简化）

但是 MySQL 不断告诉字段中的 未知列 nb_books列表。有没有什么办法使这个请求起作用吗？

感谢您的回答。

（PS：我的请求是由 Doctrine 从 DQL 生成的，因此自定义它可能会比较困难。）

原文

I've got a problem with one of my SQL requests, which is made with subqueries.

I'm trying to divide the results of two COUNT(*) requests:

SELECT (SELECT COUNT(*) FROM book) nb_books,
       (SELECT COUNT(*) FROM author) nb_authors,
       nb_books / nb_authors

(my request is much more complex and I simplified it for the example)

But MySQL keeps telling Unknown column nb_books in field list. Isn't there any way to
make this request to work?

Thanks for your answers.

(PS: my request is generated from DQL by Doctrine, so it may be more difficult to customize it.)

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§普罗旺斯的薰衣草 2024-11-07 07:32:50

两个选择：

SELECT (SELECT COUNT(*) FROM book)  as nb_books ,
       (SELECT COUNT(*) FROM author) as nb_authors,
       (SELECT COUNT(*) FROM book) /  (SELECT COUNT(*) FROM author)

或者

SELECT nb_books, nb_authors, nb_books/nb_authors
FROM (
    SELECT (SELECT COUNT(*) FROM book) nb_books,
           (SELECT COUNT(*) FROM author) nb_authors
)

我更喜欢第二种方式。如果 nb_authors 可能等于 0，您可能必须设置一个条件。

Two choices :

SELECT (SELECT COUNT(*) FROM book)  as nb_books ,
       (SELECT COUNT(*) FROM author) as nb_authors,
       (SELECT COUNT(*) FROM book) /  (SELECT COUNT(*) FROM author)

SELECT nb_books, nb_authors, nb_books/nb_authors
FROM (
    SELECT (SELECT COUNT(*) FROM book) nb_books,
           (SELECT COUNT(*) FROM author) nb_authors
)

I prefer the second way. You may have to put a condition if nb_authors could be equal to 0.

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