Question

SELECT Y/X as Z
FROM (
    SELECT
    (count(county) FROM `cleanup_site_list_2011` WHERE county= kings ) as X,
    (count(county) FROM `cleanup_site_list_2011` WHERE county= kings  AND people != 0) as Y
    FROM `cleanup_site_list_2011`
) as innertable

在上述例子中,两个“SlectT ......”表示对任何描述的 queries问(X和Y将是分类)。当我试图使用这一说法时,我发现错误。

#1054 - Unknown column  Y  in  field list

我怎么能让我的SQL认识到我设立的栏目的名称? 而且,一旦数学开始,我如何使分部分产生浮动? 还是自动这样做?

Answer 1

解决这一问题的一种办法是,在分局上列其海关名称,然后在周围地点使用这些海关名称:

SELECT 
  Y/X as Z -- moved to outer query
FROM (
  SELECT 
    (...) as X, -- assign custom names in subquery
    (...) as Y, 
  FROM `table`
) as innertable;

第二个问题:

mysql> select 4 / 3;
+--------+
| 4 / 3  |
+--------+
| 1.3333 |
+--------+
1 row in set (0.00 sec)

这是否回答? (MySQL 5)

More information here.

Answer 2

SELECT t1.x, t2.y, t2.y/t1.x z
FROM (SELECT x ...) t1, 
(SELECT y ...) t2, 
FROM `table`

友情链接