更有效的按小時分組行的方法（使用時間戳）

Question

我試圖顯示每天發生的事務日誌。我目前的方法是令人尷尬的低效率，我相信有一個更好的解決方案。這裏是我當前的查詢：

select ReaderMACAddress, 
count(typeid) as 'Total Transactions', 
SUM(CASE WHEN CAST("Timestamp" as TIME) between '05:00:00' and '11:59:59' THEN 1 ELSE 0 END) as 'Morning(5am-12pm)', 
SUM(CASE WHEN CAST("Timestamp" as TIME) between '12:00:00' and '17:59:59' THEN 1 ELSE 0 END) as 'AfternoonActivity(12pm-6pm)', 
SUM(CASE WHEN CAST("Timestamp" as TIME) between '18:00:00' and '23:59:59' THEN 1 ELSE 0 END) as 'EveningActivity(6pm-12am)', 
SUM(CASE WHEN CAST("Timestamp" as TIME) between '00:00:00' and '04:59:59' THEN 1 ELSE 0 END) as 'OtherActivity(12am-5am)' 
from Transactions 
where ReaderMACAddress = '0014f54033f5' 
Group by ReaderMACAddress; 

返回結果：

ReaderMACAddress Total Transactions Morning(5am-12pm) AfternoonActivity(12pm-6pm) EveningActivity(6pm-12am) OtherActivity(12am-5am) 
0014f54033f5    932    269     431       232       0 

（對不起，這裏的任何對齊問題）

此刻，我只想看一個單一的閱讀器，因此我指定（通過where子句）。理想情況下，它會更容易閱讀，如果時間段是在一個單柱和結果，即計數功能均在第二列初見成果，如：

Total Transactions   932 
Morning(5am-12pm)   269 
AfternoonActivity(12pm-6pm) 431 
EveningActivity(6pm-12am) 232 
OtherActivity(12am-5am)  0 

感謝所有幫助:)

Answer 1

我會首先考慮一個計算列，但我相信從以前的文章你沒有能力來改變模式。那麼觀點如何？現在

CREATE VIEW dbo.GroupedReaderView 
AS 
    SELECT ReaderMACAddress, 
    Slot = CASE WHEN t >= '05:00' AND t < '12:00' THEN 1 
       WHEN t >= '12:00' AND t < '18:00' THEN 2 
       WHEN t >= '18:00' THEN 3 ELSE 4 END 
    FROM 
    (
    SELECT ReaderMACAddress, t = CONVERT(TIME, [Timestamp]) 
    FROM dbo.Transactions 
) AS x; 

您的每-MAC地址的查詢是非常非常簡單：

SELECT Slot, COUNT(*) 
    FROM dbo.GroupedReaderView 
    WHERE ReaderMACAddress = '00...' 
    GROUP BY Slot; 

這將提供類似的結果：

1 269 
2 431 
3 232 
4  0 

你也可以添加WITH ROLLUP這將提供一個總計Slot列爲NULL：

SELECT Slot, COUNT(*) 
    FROM dbo.GroupedReaderView 
    WHERE ReaderMACAddress = '00...' 
    GROUP BY Slot 
    WITH ROLLUP; 

應該產生：

1  269 
2  431 
3  232 
4  0 
NULL 932 

你可以轉動，如果你需要，在你的表示層添加每個插槽等標籤。

你也可以這樣做，它只是讓視圖變得更加冗長，並且在你直接查詢時會拉出很多額外的數據;按字符串分組的效率也稍低。

CREATE VIEW dbo.GroupedReaderView 
AS 
    SELECT ReaderMACAddress, 
    Slot = CASE WHEN t >= '05:00' AND t < '12:00' THEN 
        'Morning(5am-12pm)' 
       WHEN t >= '12:00' AND t < '18:00' THEN 
        'Afternoon(12pm-6pm)' 
       WHEN t >= '18:00' THEN 
        'Evening(6pm-12am)' 
       ELSE 
        'Other(12am-5am)' 
       END 
    FROM 
    (
    SELECT ReaderMACAddress, t = CONVERT(TIME, [Timestamp]) 
    FROM dbo.Transactions 
) AS x; 

這些都是不一定比你有什麼更有效，但他們少重複，更容易對眼睛。 :-)

此外，如果你不想（或不能）創建一個視圖，你可以把它放到子查詢中，例如，

SELECT Slot, COUNT(*) 
    FROM 
    (
    SELECT ReaderMACAddress, 
     Slot = CASE WHEN t >= '05:00' AND t < '12:00' THEN 
        'Morning(5am-12pm)' 
        WHEN t >= '12:00' AND t < '18:00' THEN 
        'Afternoon(12pm-6pm)' 
        WHEN t >= '18:00' THEN 
        'Evening(6pm-12am)' 
        ELSE 
        'Other(12am-5am)' 
        END 
    FROM 
    (
     SELECT ReaderMACAddress, t = CONVERT(TIME, [Timestamp]) 
     FROM dbo.Transactions 
    ) AS x 
) AS y 
    WHERE ReaderMACAddress = '00...' 
    GROUP BY Slot 
    WITH ROLLUP; 

只是一個替代方案，還可以讓你們之間使用，可能還要少一些冗長：

SELECT Slot, COUNT(*) 
    FROM 
    (
    SELECT ReaderMACAddress, 
     Slot = CASE WHEN h BETWEEN 5 AND 11 THEN 'Morning(5am-12pm)' 
        WHEN h BETWEEN 12 AND 17 THEN 'Afternoon(12pm-6pm)' 
        WHEN h >= 18 THEN 'Evening(6pm-12am)' 
        ELSE 'Other(12am-5am)' 
        END 
    FROM 
    (
     SELECT ReaderMACAddress, h = DATEPART(HOUR, [Timestamp]) 
     FROM dbo.Transactions 
    ) AS x 
) AS y 
    WHERE ReaderMACAddress = '00...' 
    GROUP BY Slot 
    WITH ROLLUP; 

---

UPDATE

始終包括每個插槽即使有沒有該槽的結果：

;WITH slots(s, label, h1, h2) AS 
(
    SELECT   1, 'Morning(5am-12pm)' , 5, 11 
    UNION ALL SELECT 2, 'Afternoon(12pm-6pm)' , 12, 17 
    UNION ALL SELECT 3, 'Evening(6pm-12am)' , 18, 23 
    UNION ALL SELECT 4, 'Other(12am-5am)'  , 0, 4 
) 
SELECT s.label, c = COALESCE(COUNT(y.ReaderMACAddress), 0) 
    FROM slots AS s 
    LEFT OUTER JOIN 
    (
    SELECT ReaderMACAddress, h = DATEPART(HOUR, [Timestamp]) 
     FROM dbo.Transactions 
     WHERE ReaderMACAddress = '00...' 
) AS y 
ON y.h BETWEEN s.h1 AND s.h2 
GROUP BY s.label 
WITH ROLLUP; 

所有這些情況下的關鍵是簡化和不重複自己。即使SQL Server只執行一次，爲什麼要將時間轉換爲4次？