SQL獲得項目和明年關閉項目

Question

我有如下表（項目）

iteminfo, timestamp_start, timestamp_stop 

我需要根據時間戳來選擇一個項目：

SELECT * 
FROM items 
WHERE timestamp_start <= '2016-12-27T03:00:00' 
    AND timestamp_stop >= '2016-12-27T04:00:00' 

現在我還需要以獲得下一個最近的項目（即，具有大於所選項目的timestamp_stop的timestamp_start）。

Answer 1

您可以使用row_number來做到這一點（獲取下一個項目）。我已經把它作爲一個CTE來分清楚，但這些可以合併爲子查詢。

WITH item_rn AS 
( -- add a row number based on what we care about getting next (timestamp_start) 
    SELECT *, 
     ROW_NUMBER() OVER (ORDER BY timestamp_start) as RN 
    FROM items 
), list_in_range AS 
(-- get our base list 
    SELECT * 
    FROM item_rn 
    WHERE timestamp_start <= '2016-12-27T03:00:00' AND timestamp_stop >= '2016-12-27T04:00:00' 
), next_item AS 
(-- get the next item 
    SELECT * 
    FROM item_rn 
    WHERE rn = (SELECT MAX(rn) FROM list_in_range) + 1 
) -- combine lists for final result. 
SELECT * 
FROM list_in_range 

UNION ALL 

SELECT * 
FROM next_item 

Answer 2

我不確定您的意思是「下一個最近的項目」。如果你想下一個項目的ID，使用lead()：

SELECT i.* 
FROM (SELECT i.*, LEAD(i.item_id) OVER (ORDER BY timestamp_start) as next_item_id 
     FROM items i 
    ) i 
WHERE timestamp_start <= '2016-12-27T03:00:00' AND 
     timestamp_stop >= '2016-12-27T04:00:00'; 

作爲一個說明：

SELECT i.* 
FROM (SELECT i.*, LEAD(i) OVER (ORDER BY timestamp_start) as next_item 
     FROM items i 
    ) i 
WHERE timestamp_start <= '2016-12-27T03:00:00' AND 
     timestamp_stop >= '2016-12-27T04:00:00'; 

使用表別名指：您可以通過引用表中獲取的整個記錄除非你在Postgres中相當先進，所以我更喜歡用獨特的id來思考。

Answer 3

我想我找到了一個簡單的解決方案：

SELECT * 
     FROM items 
     WHERE timestamp_start <= '2016-12-27T04:00:00' 
      AND timestamp_stop >= '2016-12-27T04:00:00' 
UNION 
SELECT * 
     FROM items 
     WHERE timestamp_start> '2016-12-27T04:00:00' 
ORDER BY timestamp_start LIMIT 2