對於多列SQL查詢 - SUM（CASE WHEN x THEN 1 ELSE 0）

我正在查看是否有更好的方法來查詢下面。我想要做的是創建一個總結報告，按日期編制統計信息。對於多列SQL查詢 - SUM（CASE WHEN x THEN 1 ELSE 0）

SELECT CAST(Detail.ReceiptDate AS DATE) AS 'DATE' 
, SUM(CASE WHEN Detail.Type = 'TotalMailed' THEN 1 ELSE 0 END) AS 'TOTALMAILED' 
, SUM(CASE WHEN Detail.Type = 'TotalReturnMail' THEN 1 ELSE 0 END) AS 'TOTALUNDELINOTICESRECEIVED' 
, SUM(CASE WHEN Detail.Type = 'TraceReturnedMail' THEN 1 ELSE 0 END) AS 'TRACEUNDELNOTICESRECEIVED' 
FROM 
(
select SentDate AS 'ReceiptDate', 'TotalMailed' AS 'Type' 
from MailDataExtract 
where sentdate is not null 
UNION ALL 
select MDE.ReturnMailDate AS 'ReceiptDate', 'TotalReturnMail' AS 'Type' 
from MailDataExtract MDE 
where MDE.ReturnMailDate is not null 
UNION ALL 
select MDE.ReturnMailDate AS 'ReceiptDate', 'TraceReturnedMail' AS 'Type' 
from MailDataExtract MDE 
    inner join DTSharedData.dbo.ScanData SD ON SD.ScanDataID = MDE.ReturnScanDataID 
where MDE.ReturnMailDate is not null AND SD.ReturnMailTypeID = 1 
) AS Detail 
GROUP BY CAST(Detail.ReceiptDate AS DATE) 
ORDER BY 1

這僅僅是該查詢（其在一報告中所使用）的樣品作爲有一些其它列的和用於其它統計信息的邏輯是方式更加複雜。有沒有更優雅的方法來獲取這類信息/撰寫這種報告？

來源

2013-07-23 MickJuice

這是在一個進程或視圖，還是其他什麼東西？基本上，你可以引入變量並運行多個語句，還是隻是一個大的'select'語句？ –

這是一個將被用於SSRS報告的過程，所以它將基本上是一個select語句，因爲我需要返回一個結果集（對吧？） – MickJuice

是的，你最終將有一個大的'select'結束，但由於它處於proc中，因此您可以將查詢分解爲更小，更簡單的塊，並根據變量將值分配給變量。這可以在可讀性方面產生很大的不同。例如，可以將三個小型獨立查詢事先運行並將彙總結果指定給變量，而不是將這三個子查詢進行聯合或分組，而不是將這些變量分配給您的返回查詢。可能更容易閱讀和理解，並可能更好地表現。 –

我會更改查詢在以下幾個方面：

不要在子查詢的聚集。這可以利用關於表格的更多信息來優化group by。
合併第二個和第三個子查詢。他們正在聚合在同一列。這需要使用left outer join來確保所有數據都可用。
通過使用count(<fieldname>)可以消除與is null的比較。這對第二和第三個計算值很重要。
要組合第二個和第三個查詢，它需要計算mde表中的ID。這些使用mde.mdeid。

以下版本如下您例如，通過使用union all：

SELECT CAST(Detail.ReceiptDate AS DATE) AS "Date", 
     SUM(TOTALMAILED) as TotalMailed, 
     SUM(TOTALUNDELINOTICESRECEIVED) as TOTALUNDELINOTICESRECEIVED, 
     SUM(TRACEUNDELNOTICESRECEIVED) as TRACEUNDELNOTICESRECEIVED 
FROM ((select SentDate AS "ReceiptDate", COUNT(*) as TotalMailed, 
       NULL as TOTALUNDELINOTICESRECEIVED, NULL as TRACEUNDELNOTICESRECEIVED 
     from MailDataExtract 
     where SentDate is not null 
     group by SentDate 
    ) union all 
     (select MDE.ReturnMailDate AS ReceiptDate, 0, 
       COUNT(distinct mde.mdeid) as TOTALUNDELINOTICESRECEIVED, 
       SUM(case when sd.ReturnMailTypeId = 1 then 1 else 0 end) as TRACEUNDELNOTICESRECEIVED 
     from MailDataExtract MDE left outer join 
      DTSharedData.dbo.ScanData SD 
      ON SD.ScanDataID = MDE.ReturnScanDataID 
     group by MDE.ReturnMailDate; 
    ) 
    ) detail 
GROUP BY CAST(Detail.ReceiptDate AS DATE) 
ORDER BY 1;

不使用full outer join類似以下內容：

SELECT coalesce(sd.ReceiptDate, mde.ReceiptDate) AS "Date", 
     sd.TotalMailed, mde.TOTALUNDELINOTICESRECEIVED, 
     mde.TRACEUNDELNOTICESRECEIVED 
FROM (select cast(SentDate as date) AS "ReceiptDate", COUNT(*) as TotalMailed 
     from MailDataExtract 
     where SentDate is not null 
     group by cast(SentDate as date) 
    ) sd full outer join 
    (select cast(MDE.ReturnMailDate as date) AS ReceiptDate, 
      COUNT(distinct mde.mdeID) as TOTALUNDELINOTICESRECEIVED, 
      SUM(case when sd.ReturnMailTypeId = 1 then 1 else 0 end) as TRACEUNDELNOTICESRECEIVED 
    from MailDataExtract MDE left outer join 
      DTSharedData.dbo.ScanData SD 
      ON SD.ScanDataID = MDE.ReturnScanDataID 
    group by cast(MDE.ReturnMailDate as date) 
    ) mde 
    on sd.ReceiptDate = mde.ReceiptDate 
ORDER BY 1;

來源

2013-07-23 13:44:32

我認爲你應該做一個子查詢來做分組。在這種情況下，內部子查詢返回少量行，並且不需要CASE語句。因此，我認爲這將是更快：

select Detail.ReceiptDate AS 'DATE', 
     SUM(TotalMailed), 
     SUM(TotalReturnMail), 
     SUM(TraceReturnedMail) 

from 
(

select SentDate AS 'ReceiptDate', 
     count('TotalMailed') AS TotalMailed, 
     0 as TotalReturnMail, 
     0 as TraceReturnedMail 
from MailDataExtract 
where sentdate is not null 
GROUP BY SentDate 

UNION ALL 
select MDE.ReturnMailDate AS 'ReceiptDate', 
     0 AS TotalMailed, 
     count(TotalReturnMail) as TotalReturnMail, 
     0 as TraceReturnedMail 
from MailDataExtract MDE 
where MDE.ReturnMailDate is not null 
GROUP BY MDE.ReturnMailDate 

UNION ALL 

select MDE.ReturnMailDate AS 'ReceiptDate', 
     0 AS TotalMailed, 
     0 as TotalReturnMail, 
     count(TraceReturnedMail) as TraceReturnedMail 

from MailDataExtract MDE 
    inner join DTSharedData.dbo.ScanData SD 
     ON SD.ScanDataID = MDE.ReturnScanDataID 
    where MDE.ReturnMailDate is not null AND SD.ReturnMailTypeID = 1 
GROUP BY MDE.ReturnMailDate 

) as Detail 
GROUP BY Detail.ReceiptDate 
ORDER BY 1

來源

2013-07-23 13:41:01 valex

對於多列SQL查詢 - SUM（CASE WHEN x THEN 1 ELSE 0）

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