Question

假设我有一个ID列，其值为1,5,7。我可以使用什么SQL语句根据另一个值获取列中的下一个值。

示例：1之后的下一个值是5.

示例2：7之前的值是5

Answer 1

没有任何窗函数或CTE：

select
    t.id,
    (select max(t1.id) from tbl t1 where t1.id < t.id) as previd,
    (select min(t2.id) from tbl t2 where t2.id > t.id) as nextid
from tbl t

Answer 2

在SQL Server的更高版本（2012+）中，有一些很好的Windowed函数可用于处理记录。但在2008年，这些都无法获得。相反，你可以使用OUTER APPLY。这将允许您使用主查询中的值过滤子查询。

Outer Apply Query Example

WITH SampleValues AS
    (
        /* This CTE creates some sample values.
         */
        SELECT
            r.n
        FROM
            (
                VALUES
                    (1),
                    (5),
                    (7)
            ) AS r(n)
    )
SELECT
    o.n,
    prev.Previous_n,
    [next].Next_n
FROM
    SampleValues AS o
        OUTER APPLY
            (
                -- Find the previou value by looking for the TOP 1 before the current.
                SELECT TOP 1 
                    o.n     AS Original_n,
                    p.n     AS Previous_n
                FROM
                    SampleValues AS p
                WHERE
                    p.n < o.n
                ORDER BY
                    p.n DESC
            ) AS prev 
        OUTER APPLY
            (   
                -- Find the next value by looking for the TOP 1 after the current.
                SELECT TOP 1 
                    n.n     AS Original_n,
                    n.n     AS Next_n
                FROM
                    SampleValues AS n
                WHERE
                    n.n > o.n
                ORDER BY
                    n.n ASC
            )AS [next]      
;

如何获取列中的下一个值和上一个值

2 个答案: