用更好的方式编写此SQL查询的一种好方法是什么？

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 <= ?

相当令人困惑，但是我创建了此查询来查找行集的摘要。 最小和最大时间戳很简单，但是要找到速度为零而不是零的COUNT行，我做了一个丑陋的修改。 我确定有更好的方法可以做到这一点？

更新 ：“？” 会被CodeIgniter的一个不成熟的查询生成器取代。 可悲的是，它还不支持命名参数。

Answer 1

您应该包括DeviceID，这样才有意义。 尝试这个：

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

我会摆脱列子查询。 您可以像这样计算stopsDuration和tripDuration （我fuelConsumption不考虑fuelConsumption ）：

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表的单个适用行来摆脱fuelComparison子查询列 。

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 <= ?

将所有内容放在一起，您将得到（至少在纸上）应该更快的效果：

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 <= ?