SELECT 不返回数值答案

【问题标题】：SELECT does not return numeric valueSELECT 不返回数值
【发布时间】：2012-08-30 18:11:53
【问题描述】：

我有一张桌子“书”。为简单起见，这里有 3 列：

name(text) | new(boolean) | press(text)

我需要选择新书最多的出版社（出版社）。我不明白为什么 Access 显示“语法错误”。

SELECT press, COUNT(new) AS [Number of new books]
FROM books
WHERE new = TRUE
GROUP BY press
HAVING COUNT(new) = 
  SELECT MAX(s) 
  FROM 
  (   SELECT COUNT(new) AS s, press 
      FROM books
      WHERE new = TRUE
      GROUP BY press
  )

如果我只写第二部分：

  SELECT MAX(s) 
  FROM 
  (   SELECT COUNT(new) AS s, press 
      FROM books
      WHERE new = TRUE
      GROUP BY press
  )

它返回正确的值（5）

如果我只写第一部分的条件= 5，那很好。

SELECT press, COUNT(new) AS [Number of new books]
FROM books
WHERE new = TRUE
GROUP BY press
HAVING COUNT(new) = 5

我做错了什么？

【问题讨论】：

标签： sql ms-access select group-by

【解决方案1】：

第二个查询应该用括号括起来

SELECT press, COUNT(new) AS [Number of new books]
FROM books
WHERE new = TRUE
GROUP BY press
HAVING COUNT(new) = 
(
  SELECT MAX(s) 
  FROM 
  (   SELECT COUNT(new) AS s, press 
      FROM books
      WHERE new = TRUE
      GROUP BY press
  )
)

【讨论】：

【解决方案2】：

您已经有一个聚合 (GROUP BY) 查询，该查询返回每个 press 的新书数量。将其用作子查询并在按计数降序排序后获取TOP 1 行。

SELECT TOP 1
    sub.press,
    sub.CountOfNew AS [Number of new books]
FROM
    (
        SELECT
            press,
            COUNT(*) AS CountOfNew
        FROM books
        WHERE [new] = TRUE
        GROUP BY press
    ) AS sub
ORDER BY sub.CountOfNew DESC

注意，如果多个presses 与最大[Number of new books] 绑定，则此查询将返回所有绑定。（但您的原始方法也是如此。）如果您只想要其中一个关系，请在 ORDER BY 中包含一个唯一字段（例如主键）。

【讨论】：