以更好的方式寫這個SQL查詢的好方法是什麼？

Question

SELECT 
    MAX(timestamp) as end, 
    MIN(timestamp) as start, 
    (MAX(odometerKM) - MIN(odometerKM)) as distanceTravelled, 
    (SELECT COUNT(*) FROM EventData WHERE speedKPH = 0 AND timestamp >= ? AND timestamp <= ? AND deviceID = ?) as stopsDuration, 
    (SELECT COUNT(*) FROM EventData WHERE speedKPH != 0 AND timestamp >= ? AND timestamp <= ? AND deviceID = ?) as tripDuration, 
    (MAX(odometerKM) - MIN(odometerKM))/(SELECT fuelEconomy FROM Device WHERE deviceID = ?) as fuelConsumption 
FROM EventData 
WHERE deviceID = ? AND timestamp >= ? AND timestamp <= ? 

非常令人困惑，但我創建了此查詢來查找行集合的摘要。最小和最大時間戳很簡單，但要找到速度爲零而非零的行的COUNT，我做了一個醜陋的黑客。我相信有更好的方法來做到這一點？

更新：「？」請參閱由CodeIgniter的一個不成熟的查詢生成器替換。可悲的是，它尚不支持命名參數。

Answer 1

你應該包含DeviceID，所以它是有道理的。試試這個：

SELECT 
DeviceID, 
MAX(timestamp) as end, 
MIN(timestamp) as start, 
(MAX(odometerKM) - MIN(odometerKM)) as distanceTravelled, 
SUM (
    case speedKPH 
    when 0 then 1 
    else 0 
    end) as stopsDuration, 

SUM (
    case speedKPH 
    when 0 then 0 
    else 1 
    end) as tripDuration, 

(MAX(odometerKM) - MIN(odometerKM))/Device.fuelEconomy as fuelConsumption 

FROM EventData 
Join Device ON Device.deviceID = EventData.deviceID 

WHERE deviceID = ? AND timestamp >= ? AND timestamp <= ? 

GROUP BY DeviceID 

Answer 2

我擺脫了列子查詢。你可以計算stopsDuration和tripDuration這樣的（我離開了fuelConsumption現在）：

SELECT 
    MAX(timestamp) as end, MIN(timestamp) as start, 
    MAX(odometerKM) - MIN(odometerKM) as distanceTravelled, 
    COUNT(speedKPH = 0 AND timestamp >= ? AND timestamp <= ?) as stopsDuration 
    COUNT(speedKPH != 0 AND timestamp >= ? AND timestamp <= ?) as tripDuration 
FROM EventData WHERE deviceID = ? AND timestamp >= ? AND timestamp <= ? 

您可以通過交叉連接到Device表的單排適用擺脫fuelComparison子查詢的列 。

SELECT 
    (MAX(odometerKM) - MIN(odometerKM))/dv.fuelEconomy as fuelConsumption 
FROM 
    EventData, 
    (SELECT Device.fuelEconomy FROM Device WHERE DeviceId = ?) dv 
WHERE deviceID = ? AND timestamp >= ? AND timestamp <= ? 

把它放在一起，你會得到這一點，這（至少在紙）應該會更快：

SELECT 
    MAX(timestamp) as end, MIN(timestamp) as start, 
    MAX(odometerKM) - MIN(odometerKM) as distanceTravelled, 
    COUNT(speedKPH = 0 AND timestamp >= ? AND timestamp <= ?) as stopsDuration 
    COUNT(speedKPH != 0 AND timestamp >= ? AND timestamp <= ?) as tripDuration, 
    (MAX(odometerKM) - MIN(odometerKM))/dv.fuelEconomy as fuelConsumption 
FROM 
    EventData, 
    (SELECT Device.fuelEconomy FROM Device WHERE DeviceId = ?) dv 
WHERE deviceID = ? AND timestamp >= ? AND timestamp <= ?