Question

我很确定你们有一个简单而快速的解决方案来解决我的问题，但我的SQL技能是有限的，我不能自己解决。

所以我拥有的是：

新闻组：[姓名（PK）]

文章：[Id（PK）] [newsgroupName（FK）] [date：Date] [read：Boolean]

我想知道的是一个查询，它给出了每个新闻组的名称以及未读文章的数量，所有文章的数量以及最新文章的日期...... 这甚至可以在单个Select-Query中实现吗？

提前谢谢你们！

Answer 1

您可以简单地使用适当的聚合函数：

SELECT newsgroupName,
       SUM(NOT read) AS countUnread,
       COUNT(*)      AS countAll,
       MAX(date)     AS mostRecentDate
FROM Article
GROUP BY newsgroupName;

Answer 2

我猜是这样的：

SELECT name, COUNT(countUnread) AS countUnread, COUNT(countRead) AS countRead, MAX(mostRecentDateUnread) AS mostRecentDateUnread, MAX(mostRecentDateRead) AS mostRecentDateRead FROM (
    SELECT newsgroupName AS name, COUNT(newsgroupName) AS countUnread, 0 AS countRead, MAX(date) AS mostRecentDateUnread, NULL AS mostRecentDateRead
    FROM Article
    WHERE read = 0
    GROUP BY newsgroupName, read

    UNION ALL

    SELECT newsgroupName AS name, 0 AS countUnread, COUNT(newsgroupName) AS countRead, NULL AS mostRecentDateUnread, MAX(date) AS mostRecentDateRead
    FROM Article
    WHERE read = 1
    GROUP BY newsgroupName, read
)
GROUP BY name

我还没有尝试，但理论上有一些修复它可以工作。

SQLite：不同表上的两个不同的计数

2 个答案: