Postgresql在選定的日期和狀態之間選擇數據

Question

在我的Java Web應用程序中，我使用Postgresql，並且一些數據表在服務器中自動填充。在數據庫中，我有一個狀態表，如下圖所示：

我想選擇與所選擇的日期，並在車輛仍保持連接狀態之間的車輛數據。簡單地說，我想要選擇上表中綠色的數據，這意味着當首次連接= true時，我確實需要數據，而當連接=上一次連接=真時，數據連接= false。我試圖寫一個SQL語句，但我無法獲得所需的數據。

我所做的是：

select *from status where vehicleId='redcar' and 
date >= '2014-02-28 00:00:00' and date <= '2014-02-28 23:59:59' and ... 

我怎麼能獲得所請求的數據？

Answer 1

WITH cte AS 
    (SELECT statusId, vehicleId, connected, date, 
      (connected <> LAG(connected) OVER (PARTITION BY vehicleId 
               ORDER BY date) 
      ) AS status_changed 
    FROM status 
    WHERE vehicleId = 'redcar' 
     AND date >= DATE '2014-02-28' 
     AND date < DATE '2014-02-28' + interval '1 day' 
) 
SELECT statusId, vehicleId, connected, date 
FROM cte 
WHERE status_changed 
    OR connected AND status_changed IS NULL 
ORDER BY date ; 

測試在SQL-Fiddle

Answer 2

你可以做到這一點使用Gaps and Islands邏輯：

SELECT VehicleID, Connected, MIN(Date) AS Date 
FROM ( SELECT *, 
        DENSE_RANK() OVER(PARTITION BY VehicleID ORDER BY Date) - 
         DENSE_RANK() OVER(PARTITION BY VehicleID, Connected ORDER BY Date) AS GroupingSet, 
        MIN(CASE WHEN Connected THEN Date END) OVER(PARTITION BY VehicleID) AS FirstConnected 
      FROM status 
      WHERE VehicleID = 'redcar' 
      AND  date >= '2014-02-28 00:00:00' 
      AND  date < '2014-03-01 00:00:00' 
     ) s 
WHERE Date > FirstConnected 
GROUP BY VehicleID, Connected, GroupingSet 

Example on SQL Fiddle

如果您還需要檢索StatusID你將需要添加一個進一步排序功能，只只選擇第一行：

SELECT StatusID, 
     VehicleID, 
     Connected, 
     Date 
FROM ( SELECT StatusID, 
        VehicleID, 
        Connected, 
        Date, 
        ROW_NUMBER() OVER(PARTITION BY VehicleID, Connected, GroupingSet ORDER BY Date) AS RowNumber 
      FROM ( SELECT *, 
           DENSE_RANK() OVER(PARTITION BY VehicleID ORDER BY Date) - 
            DENSE_RANK() OVER(PARTITION BY VehicleID, Connected ORDER BY Date) AS GroupingSet, 
           MIN(CASE WHEN Connected THEN Date END) OVER(PARTITION BY VehicleID) AS FirstConnected 
         FROM status 
         WHERE VehicleID = 'redcar' 
         AND  date >= '2014-02-28 00:00:00' 
         AND  date < '2014-03-01 00:00:00' 
        ) s 
      WHERE Date > FirstConnected 
     ) s 
WHERE RowNumber = 1; 

Example on SQL Fiddle

或者使用DISTINCT ON：

SELECT DISTINCT ON (VehicleID, Connected, GroupingSet) 
     StatusID, 
     VehicleID, 
     Connected, 
     Date 
FROM ( SELECT *, 
        DENSE_RANK() OVER(PARTITION BY VehicleID ORDER BY Date) - 
         DENSE_RANK() OVER(PARTITION BY VehicleID, Connected ORDER BY Date) AS GroupingSet, 
        MIN(CASE WHEN Connected THEN Date END) OVER(PARTITION BY VehicleID) AS FirstConnected 
      FROM status 
      WHERE VehicleID = 'redcar' 
      AND  date >= '2014-02-28 00:00:00' 
      AND  date < '2014-03-01 00:00:00' 
     ) s 
WHERE Date > FirstConnected 
ORDER BY VehicleID, Connected, GroupingSet 

Example on SQL Fiddle

Answer 3

您可以用window function做到這一點。

事情是這樣的：

with status_changes as(
     select 
      id, 
      vehicleid, 
      connected, 
      connected != lag(connected) 
       over (partition by vehicleid 
         order by date asc) as has_changed 
     from STATUS 
) 
select 
    id, 
    vehicleid, 
    connected, 
    date 
from status_changes 
where has_changed = true 
     and vehicle = 'redcar' 
     and date between '2014-02-28 00:00:00' and '2014-02-28 23:59:59'; 

• 滯後（狀態）將返回在它之前的狀態（我們的分區中）。

• 分區由vehicleid（與由日期的順序排列）保證了我們的滯後（）返回同一vehicleid的行。

見window functions列表以獲得更多關於滯後（）和相關功能。