SQL获得项目和明年关闭项目

Question

我有如下表（项目）

iteminfo, timestamp_start, timestamp_stop 

我需要根据时间戳来选择一个项目：

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

现在我还需要以获得下一个最近的项目（即，具有大于所选项目的timestamp_stop的timestamp_start）。

Answer 1

您可以使用row_number来做到这一点（获取下一个项目）。我已经把它作为一个CTE来分清楚，但这些可以合并为子查询。

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

我不确定您的意思是“下一个最近的项目”。如果你想下一个项目的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'; 

作为一个说明：

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'; 

使用表别名指：您可以通过引用表中获取的整个记录除非你在Postgres中相当先进，所以我更喜欢用独特的id来思考。

Answer 3

我想我找到了一个简单的解决方案：

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