sql - 根据给定的声誉获取最近的特权

Question

我有一个业务场景，其中几乎没有边缘情况。让我用 Stack Overflow Privileges 来解释一下数据。

请查找权限架构创建和示例数据:https://rextester.com/KQZS91498

根据给定的声誉输入，我需要找到最近的权限。即小于给定声誉的最近的特权和接下来可以实现的特权。

示例:如果我提供的声誉为 7276，我需要以下权限作为输出:

Id  Reputation  PrivilegeName
------------------------------------------
22  5000        approve tag wiki edits
23  10000       access to moderator tools

我使用以下查询来实现它。

DECLARE @MyReputation AS INT = 7276;

DECLARE @FromId AS INT = 0;
DECLARE @ToId AS INT = 0;

SELECT @FromId = MAX(Id) FROM @Privilege
WHERE Reputation > 0 AND Reputation <= @MyReputation;

SELECT @ToId = MIN(Id) FROM @Privilege
WHERE @MyReputation > 0 AND @MyReputation < Reputation;

SELECT Id, Reputation, PrivilegeName
FROM @Privilege
WHERE Id IN (@FromId, @ToId)
ORDER BY Id;

它给了我预期的结果。

请找到相同的可执行查询:https://rextester.com/PDEXOM92503 .

<小时/>

由于我使用聚合函数来获取 ID，因此如果声誉拥有多个特权，则该函数不起作用。

这里的声誉10包含两个特权。而且将来有可能，它可能会拥有三个或更多的权限。

所以期望是，如果我提供的声誉输入为 10 或 13，我需要的输出为:

Id  Reputation  PrivilegeName
----------------------------------------------
3   10          remove new user restrictions
4   10          create wiki posts
5   15          flag posts
6   15          vote up

对于945的声誉输入:

Id  Reputation  PrivilegeName
------------------------------------------
15  500         access review queues
16  1000        established user
17  1000        create gallery chat rooms

即，基于给定信誉输入的最接近的可能权限。

该案例适用于像100、1000这样的声誉，这些声誉对于同一声誉具有多个特权。

实现上述期望的最佳方式是什么？

Answer 1

您也可以使用 UNION ALL 执行以下操作。

;WITH cte 
     AS (SELECT *, 
                reputation - @MyReputation DIFF 
         FROM   @Privilege) 
SELECT * 
FROM   cte 
WHERE  diff = (SELECT Max(diff) 
               FROM   cte 
               WHERE  diff <= 0) 
UNION ALL
SELECT * 
FROM   cte 
WHERE  diff = (SELECT Min(diff) 
               FROM   cte 
               WHERE  diff > 0) 

Online Demo

上面的查询也可以使用CASE WHEN编写，如下所示

;WITH cte 
     AS (SELECT *, 
                reputation - @MyReputation diff, 
                Max(CASE 
                      WHEN reputation - @MyReputation <= 0 THEN 
                      reputation - @MyReputation 
                    END) 
                  OVER()                   mind, 
                Min(CASE 
                      WHEN reputation - @MyReputation > 0 THEN 
                      reputation - @MyReputation 
                    END) 
                  OVER()                   maxd 
         FROM   @Privilege) 

SELECT Id,Reputation,PrivilegeName,DetailedDescription 
FROM   cte 
WHERE  diff in (mind,maxd)