根据当前步骤编号获取上一步和下一步唯一ID

Question

简单的问题，但我似乎找不到简单的解决方案：

在给定以下数据的情况下，根据当前步骤编号获取上一步和下一步唯一 HEX ID 的最有效方法是什么：

----+-------------+----------------
ID  | UnqID   |步骤编号 |
----+-------------+----------------
21 | BcDeF   | 1        |
22 | GhIjKL   | 2        |
23 | MnOPq  | 3        |
24 | | RsTuV   | 4        |
25 | wXyZa   | 5        |
----+-------------+----------------

例如：
假设提供的步骤是3，我如何获得2 和4 的唯一HEX ID？

谢谢！

---

编辑
这是我目前正在使用的，但对我来说似乎效率不高？？

SELECT
    nxt.stepnum AS NextStep,
    nxt.unqID AS NextUnqID,
    prv.stepnum AS PrevStep,
    prv.unqID AS PrevUnqID
FROM foo w,
(
 SELECT stepnum, unqID FROM foo WHERE stepnum > 3 ORDER BY stepnum LIMIT 1
) AS nxt
,
(
 SELECT stepnum, unqID FROM foo WHERE stepnum < 3 AND ORDER BY stepnum DESC LIMIT 1
) AS prv
WHERE w.stepnum = 3

Answer 1

我修改了您的查询。虽然它有点嵌套，但它应该由非常简单的 sql 引擎索引查找组成（理论上......）

SELECT
    nxt.stepnum AS NextStep,
    nxt.unqID   AS NextUnqID,
    prv.stepnum AS PrevStep,
    prv.unqID   AS PrevUnqID

FROM (SELECT NULL) AS dummy -- dummy table to LEFT JOIN to

LEFT JOIN
( SELECT stepnum, unqID FROM foo
  WHERE stepnum = (SELECT MIN(stepnum)
                   FROM foo
                   WHERE stepnum > 5 )
) AS nxt ON true

LEFT JOIN
( SELECT stepnum, unqID FROM foo
  WHERE stepnum = (SELECT MAX(stepnum)
                   FROM foo
                   WHERE stepnum < 5 )
) AS prv ON true