如何在计数查询的结果中包含 0答案

【问题标题】：How to include 0 in the result of count query如何在计数查询的结果中包含 0
【发布时间】：2016-01-28 23:07:24
【问题描述】：

我有 4 个表，存储 4 种请求：休假 (TO)、会议 (MT)、PO 和旅行 (TR)。

我想统计过去 30 天内每个表中每种类型的请求总数：

  SELECT [requestType], COUNT ([requestType]) As 'Count' 
  FROM [Timeoff] 
  WHERE [requestType] = 'TO' AND CAST([timeoffCreatedTime] AS DATE) >= CAST(DateAdd(DAY,-30,Getdate()) AS DATE) GROUP BY [requestType]
  UNION ALL
  SELECT [requestType], COUNT ([requestType]) As 'Count' 
  FROM [Meeting] 
  WHERE [requestType] = 'MT' AND CAST([meetingCreatedTime] AS DATE) >= CAST(DateAdd(DAY,-30,Getdate()) AS DATE) GROUP BY [requestType]
  UNION ALL
  SELECT [requestType], COUNT ([requestType]) As 'Count' 
  FROM [PO] 
  WHERE [requestType] = 'PO' AND CAST([poCreatedTime] AS DATE) >= CAST(DateAdd(DAY,-30,Getdate()) AS DATE) GROUP BY [requestType]
  UNION ALL
  SELECT [requestType], COUNT ([requestType]) As 'Count' 
  FROM [Travel] 
  WHERE [requestType] = 'TR' AND CAST([travelCreatedTime] AS DATE) >= CAST(DateAdd(DAY,-30,Getdate()) AS DATE) GROUP BY [requestType]

问题是，如果计数为 0，那么它根本不会出现在结果中，例如，如果会议请求的计数 = 0，那么我只有这个结果：

我如何在结果中包含 0 值，所以我会有类似的东西（如果 Meeting MT count = 0）：

requestType --- 计数

到 ------------- 30

MT ------------- 0

PO -------------19

TR -------------9

【问题讨论】：

为什么要编写 Group By 子句？我认为不需要作为我的书面解决方案

标签： sql sql-server join count aggregate-functions

【解决方案1】：

您必须从查询中删除 GROUP BY，这不是必需的！您的查询应该是：

SELECT 'TO' AS [requestType], COUNT ([requestType]) As 'Count' 
  FROM [Timeoff] 
  WHERE [requestType] = 'TO' AND CAST([timeoffCreaime] ATE) >= CASt(DAY,-30,Gte()) ATE)
  UNION ALL
  SELECT 'Meeting' AS [requestType], COUNT ([requestType]) As 'Count' 
  FROM [Meeting] 
  WHERE [requestType] = 'Meeting' AND CAST([meetingCreaime] ATE) >= CASt(DAY,-30,Gte()) ATE)
  UNION ALL
  SELECT 'PO' AS [requestType], COUNT ([requestType]) As 'Count' 
  FROM [PO] 
  WHERE [requestType] = 'PO' AND CAST([poCreaime] ATE) >= CASt(DAY,-30,Gte()) ATE)
  UNION ALL
  SELECT 'TR' AS [requestType], COUNT ([requestType]) As 'Count' 
  FROM [Travel] 
  WHERE [requestType] = 'TR' AND CAST([travelCreaime] ATE) >= CASt(DAY,-30,Gte()) ATE)

【讨论】：

它已经以这种方式硬编码，他需要在 WHERE 过滤器中使用它，因为我不知道他的业务逻辑。
我回滚了编辑以将其恢复到原始状态。要使您的代码正常工作，您需要从 select 语句中删除 RequestType 并对 RequestType 进行硬编码。
@AnupAgrawal 为什么要编辑我的解决方案，其中包含 requestType ... 然后要求这样做？ :) Ronaldinho 代码工作正常，只需要删除 GROUP BY 子句即可获得结果中的 0 计数。我认为这应该是一个正确的答案。谢谢
这里可以看到修改历史。 stackoverflow.com/posts/35074523/revisions 。您的代码没有硬编码，根据您的要求，我回滚了包含硬编码的编辑。
@AnupAgrawal 我现在明白你的意思了，我把硬编码回来了 :) 谢谢

【解决方案2】：

您可以对每个查询进行外部联接，例如 (select 1)

SELECT [requestType], COUNT ([requestType]) As 'Count' 
  FROM (select 1 as foo) bar
  LEFT JOIN [CTEite].[dbo].[Timeoff] ON 1=1
  WHERE [requestType] = 'TO' AND CAST([timeoffCreaime] ATE) >= CASt(DAY,-

或 UNION 和 sum

WITH foo AS(
SELECT 'TO' as [requestType], 0 as [Count]
UNION ALL
SELECT 'MT', 0
UNION ALL
....
)
SELECT [requestType], sum([Count])
FROM
(SELECT [requestType], COUNT ([requestType]) As 'Count' 
  FROM [CTEite].[dbo].[Timeoff] 
  WHERE [requestType] = 'TO' AND CAST([timeoffCreaime] ATE) >= CASt(DAY,-30,Gte()) ATE) GROUP BY [requestType]
  UNION ALL
  SELECT [requestType], COUNT ([requestType]) As 'Count' 
  FROM [CTEite].[dbo].[Meeting] 
  WHERE [requestType] = 'Meeting' AND CAST([meetingCreaime] ATE) >= CASt(DAY,-30,Gte()) ATE) GROUP BY [requestType]
  UNION ALL
  SELECT [requestType], COUNT ([requestType]) As 'Count' 
  FROM [CTEite].[dbo].[PO] 
  WHERE [requestType] = 'PO' AND CAST([poCreaime] ATE) >= CASt(DAY,-30,Gte()) ATE) GROUP BY [requestType]
  UNION ALL
  SELECT [requestType], COUNT ([requestType]) As 'Count' 
  FROM [CTEite].[dbo].[Travel] 
  WHERE [requestType] = 'TR' AND CAST([travelCreaime] ATE) >= CASt(DAY,-30,Gte()) ATE) GROUP BY [requestType]
 UNION SELECT * FROM foo)
GROUP BY [requestType]

【讨论】：