以更好的方式写这个SQL查询的好方法是什么？

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，但我创建了此查询来查找行集合的摘要。最小和最大时间戳很简单，但要找到速度为零而非零的行的COUNT，我做了一个丑陋的黑客。我相信有更好的方法来做到这一点？

更新：“？”请参阅由CodeIgniter的一个不成熟的查询生成器替换。可悲的是，它尚不支持命名参数。

Answer 1

你应该包含DeviceID，所以它是有道理的。试试这个：

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

我摆脱了列子查询。你可以计算stopsDuration和tripDuration这样的（我离开了fuelConsumption现在）：

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 <= ? 

您可以通过交叉连接到Device表的单排适用摆脱fuelComparison子查询的列 。

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，你会得到这一点，这（至少在纸）应该会更快：

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 <= ?