獲取前行標識，而在ID

Question

排序沒有提到下面如何從表以前&下一個ID具有結構：

+----+---------+---------------------+ 
| id | urgency | timestamp   | 
+----+---------+---------------------+ 
| 1 | 0  | 2013-01-01 00:00:00 | 
| 2 | 2  | 2013-01-01 00:00:00 | 
| 3 | 1  | 2013-01-05 09:30:00 | 
| 4 | 2  | 2013-01-01 00:00:00 | 
| 5 | 2  | 2013-01-01 00:00:00 | 
| 6 | 1  | 2013-01-06 10:00:00 | 
| 7 | 0  | 2013-01-01 00:00:00 | 
| 8 | 0  | 2013-01-03 00:00:00 | 
| 9 | 1  | 2013-02-01 13:30:00 | 
| 10 | 0  | 2013-01-04 00:00:00 | 
+----+---------+---------------------+ 

表進行排序如下：尿急遞增，時間戳遞增， ID ASC

這裏是排序表：

+----+---------+---------------------+ 
| id | urgency | timestamp   | 
+----+---------+---------------------+ 
| 1 | 0  | 2013-01-01 00:00:00 | 
| 7 | 0  | 2013-01-01 00:00:00 | 
| 8 | 0  | 2013-01-03 00:00:00 | 
| 10 | 0  | 2013-01-04 00:00:00 | 
| 3 | 1  | 2013-01-05 09:30:00 | 
| 6 | 1  | 2013-01-06 10:00:00 | 
| 9 | 1  | 2013-02-01 13:30:00 | <= CURRENT_ID 
| 2 | 2  | 2013-01-01 00:00:00 | 
| 4 | 2  | 2013-01-01 00:00:00 | 
| 5 | 2  | 2013-01-01 00:00:00 | 
+----+---------+---------------------+ 

有沒有辦法從MySQL選擇一些地方的位置CURRENT_ID - 1或CURRENT_ID + 1？

我能做的是執行一個簡單的查詢：

SELECT 
    id 
FROM 
    MY_TABLE 
ORDER BY 
    urgency asc, 
    timestamp asc, 
    id asc 

通過創建結果PHP一個循環，並尋找合適的位置，但是這是一個表，將會增加非常快。因此，這不是一個選項...希望有另一種解決方案，您可以建議

Answer 1

對於以前：

SELECT prev.id 
FROM my_table current 
JOIN my_table prev 
    ON (prev.urgency < current.urgency) 
    OR (prev.urgency = current.urgency 
     AND (prev.timestamp < current.timestamp 
      OR (prev.timestamp = current.timestamp AND prev.id < current.id))) 
WHERE current.id = @currentId 
ORDER BY prev.urgency desc, prev.timestamp desc, prev.id desc 
LIMIT 1 

對於未來：

SELECT next.id 
FROM my_table current 
JOIN my_table next 
    ON (next.urgency > current.urgency) 
    OR (next.urgency = current.urgency 
     AND (next.timestamp > current.timestamp 
      OR (next.timestamp = current.timestamp AND next.id > current.id))) 
WHERE current.id = @currentId 
ORDER BY next.urgency asc, next.timestamp asc, next.id asc 
LIMIT 1 

Sqlfiddle這裏。

試圖讓它們在一個查詢中更具挑戰性，但可以使用類似的方法使用嵌套分組代替LIMIT來完成。我懷疑你會在這樣一個複雜的查詢中看到很多性能優勢，你肯定會很難保持它...