有没有办法可以从 SQL 查询中获取总数？

Question

这是我的查询：

SELECT CG.Id, CG.Name, CG.IsToggled, COUNT(*) AS TotalWordCount
FROM CategoryGroup AS CG
JOIN Category AS C ON CG.Id = C.GroupId
JOIN Phrase AS P ON C.Id = P.CategoryId
GROUP BY CG.Id
ORDER BY CG.Name

我需要做的是获取 TotalWordCount 列的总数其中 CG.IsToggled = 1

这是否可能在同一个查询中，或者有什么方法可以用两个查询来做到这一点。如果两个 SQL 语句的值与所有 TotalWordCount 加在一起的值相同，则它们是可以的。

Answer 1

我需要做的是获取 CG.IsToggled = 1 的 TotalWordCount 列的总数

您不能在同一个查询中进行总计（聚合的聚合）。但是，您可以在这样的子查询中执行此操作：

SELECT CG.Id, CG.Name, CG.IsToggled, SUM(c2.TotalWordCount) AS TotalWordCount
FROM CategoryGroup AS CG
INNER JOIN
( 
   SELECT Id, Name, COUNT(*) AS TotalWordCount
   FROM CategoryGroup
   WHERE IsToggled = 1
   GROUP BY Id, Name
) AS c2 ON c2.Id = CG.Id AND c2.Name = CG.Name
JOIN Category AS C ON CG.Id = C.GroupId
JOIN Phrase AS P ON C.Id = P.CategoryId
GROUP BY CG.Id, CG.Name, CG.IsToggled
ORDER BY CG.Name

请注意：您可能需要使用LEFT JOIN 来将带有IsToggled = 0 的人也包含在查询中：

SELECT CG.Id, CG.Name, CG.IsToggled, SUM(COALESCE(c2.TotalWordCount, 0)) AS TotalWordCount
FROM CategoryGroup AS CG
JOIN Category AS C ON CG.Id = C.GroupId
JOIN Phrase AS P ON C.Id = P.CategoryId
LEFT JOIN
( 
   SELECT Id, Name, COUNT(*) AS TotalWordCount
   FROM CategoryGroup
   WHERE IsToggled = 1
   GROUP BY Id, Name
) AS c2 ON c2.Id = CG.Id AND c2.Name = CG.Name
GROUP BY CG.Id, CG.Name, CG.IsToggled
ORDER BY CG.Name

Answer 2

你可以通过window function解决这个问题

SELECT CG.Id, CG.Name, CG.IsToggled, COUNT(*) AS TotalWordCount,
    COUNT(*) OVER (PARTITION BY CG.id) as TotalTotalWordCount
FROM CategoryGroup AS CG
JOIN Category AS C ON CG.Id = C.GroupId
JOIN Phrase AS P ON C.Id = P.CategoryId
GROUP BY CG.Id
ORDER BY CG.Name

假设这实际上是 Microsoft SQL Server（这意味着发布的原始查询会出错，因为它在您的 GROUP BY 中没有 CG.Name）。