Sql 按优先级返回基于可空列的数据的存储过程

我有一个名为

ClientUrls

的表，其结构如下：

+------------+----------------+----------+
| ColumnName |    DataType    | Nullable |
+------------+----------------+----------+
| ClientId   | INT            | No       |
| CountryId  | INT            | Yes      |
| RegionId   | INT            | Yes      |
| LanguageId | INT            | Yes      |
| URL        | NVARCHAR(2048) | NO       |
+------------+----------------+----------+

我有一个存储过程

up\u GetClientUrls

，它接受以下参数：

@ClientId INT
@CountryId INT
@RegionId INT
@LanguageId INT

有关程序的信息

所有参数都是proc所必需的，并且没有一个参数是空的

该过程的目的是基于预定义的优先级返回表中的单个匹配行。优先顺序为ClientId>Country>Region>Language

ClientUrls表中的三个列可为空。如果一列包含空值，则表示“全部”。e、 g.如果LanguageId为空，则它表示“所有语言”。因此，如果我们向proc发送一个LanguageId为5的，我们会首先查找它，否则我们会尝试找到一个为NULL的

优先级矩阵（1为第一位）

以下是一些示例数据：

+----------+-----------+----------+------------+-------------------------------+
| ClientId | CountryId | RegionId | LanguageId |             URL               |
+----------+-----------+----------+------------+-------------------------------+
|        1 |         1 | 1        | 1          | http://www.Website.com        |
|        1 |         1 | 1        | NULL       | http://www.Otherwebsite.com   |
|        1 |         1 | NULL     | 2          | http://www.Anotherwebsite.com |
+----------+-----------+----------+------------+-------------------------------+

示例存储过程调用

EXEC up_GetClientUrls   @ClientId = 1
                        ,@CountryId = 1
                        ,@RegionId = 1
                        ,@LanguageId = 2

预期响应（基于示例数据）

返回此行是因为在空RegionId上匹配正确的LanguageId比在空LanguageId上匹配正确的RegionId优先级更高

下面是proc的代码（它可以工作）。为了回答我的问题，有没有更好的方法来写这个？如果我将来扩展这个表，我将继续乘以UNION语句的数量，因此它实际上是不可伸缩的

实际存储过程

CREATE PROC up_GetClientUrls
    (
        @ClientId       INT
        ,@CountryId     INT
        ,@RegionId      INT
        ,@LanguageId    INT
    )
AS
    BEGIN

        SELECT TOP 1
            prioritised.ClientId
            ,prioritised.CountryId
            ,prioritised.RegionId
            ,prioritised.LanguageId
            ,prioritised.URL
        FROM
        (
            SELECT
                c.ClientId
                ,c.CountryId
                ,c.RegionId
                ,c.LanguageId
                ,c.URL
                ,1  [priority]
            FROM ClientUrls c
            WHERE c.ClientId = @ClientId
            AND c.CountryId = @CountryId
            AND c.RegionId = @RegionId
            AND c.LanguageId = @LanguageId
            UNION
                SELECT
                    c.ClientId
                    ,c.CountryId
                    ,c.RegionId
                    ,c.LanguageId
                    ,c.URL
                    ,2  [priority]
                FROM ClientUrls c
                WHERE c.ClientId = @ClientId
                AND c.CountryId IS NULL
                AND c.RegionId = @RegionId
                AND c.LanguageId = @LanguageId
            UNION
                SELECT
                    c.ClientId
                    ,c.CountryId
                    ,c.RegionId
                    ,c.LanguageId
                    ,c.URL
                    ,3  [priority]
                FROM ClientUrls c
                WHERE c.ClientId = @ClientId
                AND c.CountryId = @CountryId
                AND c.RegionId IS NULL
                AND c.LanguageId = @LanguageId
            UNION
                SELECT
                    c.ClientId
                    ,c.CountryId
                    ,c.RegionId
                    ,c.LanguageId
                    ,c.URL
                    ,4  [priority]
                FROM ClientUrls c
                WHERE c.ClientId = @ClientId
                AND c.CountryId IS NULL
                AND c.RegionId IS NULL
                AND c.LanguageId = @LanguageId
            UNION
                SELECT
                    c.ClientId
                    ,c.CountryId
                    ,c.RegionId
                    ,c.LanguageId
                    ,c.URL
                    ,5  [priority]
                FROM ClientUrls c
                WHERE c.ClientId = @ClientId
                AND c.CountryId = @CountryId
                AND c.RegionId = @RegionId
                AND c.LanguageId IS NULL
            UNION
                SELECT
                    c.ClientId
                    ,c.CountryId
                    ,c.RegionId
                    ,c.LanguageId
                    ,c.URL
                    ,6  [priority]
                FROM ClientUrls c
                WHERE c.ClientId = @ClientId
                AND c.CountryId IS NULL
                AND c.RegionId = @RegionId
                AND c.LanguageId IS NULL
            UNION
                SELECT
                    c.ClientId
                    ,c.CountryId
                    ,c.RegionId
                    ,c.LanguageId
                    ,c.URL
                    ,7  [priority]
                FROM ClientUrls c
                WHERE c.ClientId = @ClientId
                AND c.CountryId IS NULL
                AND c.RegionId IS NULL
                AND c.LanguageId IS NULL
        ) prioritised
        ORDER BY prioritised.[Priority]

    END

---

您可以将where子句更改为：

AND (c.CountryID = @CountryID OR c.CountryID IS NULL)

编码方面，它的代码更少。

---

但调整问题更大。

未经测试，但您可以执行以下操作：

SELECT TOP 1 c.ClientId,
        c.CountryId,
        c.RegionId,
        c.LanguageId,
        c.URL
FROM ClientUrls c
ORDER BY CASE 
            WHEN c.ClientId = @ClientId
                THEN 1000
            ELSE 0
            END + 
        CASE 
            WHEN c.CountryId = @CountryId
                THEN 200
            WHEN c.CountryId IS NULL
                THEN 100
            ELSE 0
            END + 
        CASE 
            WHEN c.RegionId = @RegionId
                THEN 20
            WHEN c.CountryId IS NULL
                THEN 10
            ELSE 0
            END +  
        CASE 
            WHEN c.LanguageId = @LanguageId
                THEN 2
            WHEN c.CountryId IS NULL
                THEN 1
            ELSE 0
            END DESC

WITH priorities as     (SELECT
                c.ClientId
                ,c.CountryId
                ,c.RegionId
                ,c.LanguageId
                ,c.URL
                ,COALESCE(
                          NULLIF(c.CountryId,@CountryId),
                          NULLIF(c.RegionId,@RegionId),
                          NULLIF(c.LanguageId,@LanguageId),
                          1000000)
                + ISNULL(c.CountryId,200000)  
                + ISNULL(c.RegionId,100000) 
                + COALESCE(c.CountryId,RegionId,40000) 
                + ISNULL(c.LanguageId,10000) 
                + COALESCE(c.CountryId,c.LanguageId,4000) 
                + COALESCE(c.CountryId,c.RegionId,c.LanguageId,1000)
                [priority]
            FROM ClientUrls c
            WHERE c.ClientId = @ClientId
            AND (c.CountryId = @CountryId
            OR c.RegionId = @RegionId
            OR c.LanguageId = @LanguageId)
            )
SELECT TOP 1 ClientId,CountryId,RegionId,LanguageId,URL FROM priorities ORDER BY priority DESC

通过为每个匹配项指定一个值并选择最高值，可以减少所需的代码。但您将增加所需案例陈述的数量，而不是工会的数量

---

这也可以是一个函数，而不是存储过程。因此，它可以更容易地用于其他查询的

另一种方法可能是尝试操纵

NULL

值来创建继承权，如下所示：

SELECT TOP 1 c.ClientId,
        c.CountryId,
        c.RegionId,
        c.LanguageId,
        c.URL
FROM ClientUrls c
ORDER BY CASE 
            WHEN c.ClientId = @ClientId
                THEN 1000
            ELSE 0
            END + 
        CASE 
            WHEN c.CountryId = @CountryId
                THEN 200
            WHEN c.CountryId IS NULL
                THEN 100
            ELSE 0
            END + 
        CASE 
            WHEN c.RegionId = @RegionId
                THEN 20
            WHEN c.CountryId IS NULL
                THEN 10
            ELSE 0
            END +  
        CASE 
            WHEN c.LanguageId = @LanguageId
                THEN 2
            WHEN c.CountryId IS NULL
                THEN 1
            ELSE 0
            END DESC

WITH priorities as     (SELECT
                c.ClientId
                ,c.CountryId
                ,c.RegionId
                ,c.LanguageId
                ,c.URL
                ,COALESCE(
                          NULLIF(c.CountryId,@CountryId),
                          NULLIF(c.RegionId,@RegionId),
                          NULLIF(c.LanguageId,@LanguageId),
                          1000000)
                + ISNULL(c.CountryId,200000)  
                + ISNULL(c.RegionId,100000) 
                + COALESCE(c.CountryId,RegionId,40000) 
                + ISNULL(c.LanguageId,10000) 
                + COALESCE(c.CountryId,c.LanguageId,4000) 
                + COALESCE(c.CountryId,c.RegionId,c.LanguageId,1000)
                [priority]
            FROM ClientUrls c
            WHERE c.ClientId = @ClientId
            AND (c.CountryId = @CountryId
            OR c.RegionId = @RegionId
            OR c.LanguageId = @LanguageId)
            )
SELECT TOP 1 ClientId,CountryId,RegionId,LanguageId,URL FROM priorities ORDER BY priority DESC

这很容易（如果我理解正确的话）。您只需要很少的代码就可以做到这一点。此外，如果需要，它将很容易扩展

下面是一个工作示例

--Make a table
CREATE TABLE #ClientUrls (ClientId INT NOT NULL,CountryId INT NULL,RegionId INT NULL,LanguageId INT NULL,URL NVARCHAR(2048) NOT NULL)

--Put some data into it
INSERT INTO #ClientUrls (ClientId, CountryId, RegionId, LanguageId, URL)
VALUES
(1,1,1,1,'http://www.Website.com'),
(1,1,1,NULL,'http://www.Otherwebsite.com'),
(1,1,NULL,2,'http://www.Anotherwebsite.com')

--This would all be in your proc
----------------------------------------------
DECLARE @ClientId       INT = 1
DECLARE @CountryId      INT = 1
DECLARE @RegionId       INT = 1
DECLARE @LanguageId     INT = 2

--This is the interesting bit
----------------------------------------------
SELECT TOP 1 C.*

FROM    #ClientUrls AS C
ORDER BY 
    --Order the ones with the best hit count near the top
   IIF(ISNULL(C.ClientId,  @ClientId)   = @ClientId  ,1,0) +            
   IIF(ISNULL(C.CountryId, @CountryId)  = @CountryId ,2,0) +
   IIF(ISNULL(C.RegionId,  @RegionId)   = @RegionId  ,4,0) +
   IIF(ISNULL(C.LanguageId,@LanguageId) = @LanguageId,8,0) DESC,

    --Order the ones with the least nulls of each hit count near the top
   IIF(C.ClientId   IS NULL,0,1) +                                              
   IIF(C.CountryId  IS NULL,0,2) +
   IIF(C.RegionId   IS NULL,0,4) +
   IIF(C.LanguageId IS NULL,0,8) DESC

DROP TABLE #ClientUrls

就这样。在较旧版本的SQL中，您不能使用IIF，但如果需要，您可以使用case语句替换IIF

它是这样工作的

每个匹配项都有一个值（有点像二进制数） 然后根据每个匹配项，我们使用值或0（如果不匹配） 把总数加起来，我们总是能选出最好的比赛组合

value          1           2           4         8            Total value 
+---------+----------+-----------+----------+------------+
| Ranking | ClientId | CountryId | RegionId | LanguageId |
+---------+----------+-----------+----------+------------+
|       1 | NOT NULL | NOT NULL  | NOT NULL | NOT NULL   |       15
|       2 | NOT NULL | NULL      | NOT NULL | NOT NULL   |       13
|       3 | NOT NULL | NOT NULL  | NULL     | NOT NULL   |       11  
|       4 | NOT NULL | NULL      | NULL     | NOT NULL   |       9
|       5 | NOT NULL | NOT NULL  | NOT NULL | NULL       |       7
|       6 | NOT NULL | NULL      | NOT NULL | NULL       |       5
|       7 | NOT NULL | NULL      | NULL     | NULL       |       1
+---------+----------+-----------+----------+------------+

我只是更新了它，以确保您通过null选项获得非null版本

---

如果编辑结果以返回多于前1的结果，则可以按正确顺序查看项目。即，如果将语言从2更改为1，您将在1,1,1空选项上获得1,1,1行

您的客户端id在表中是唯一的吗？我的意思是如果我能得到

[Client\u id 1 Country 1]，[Client\u id 1，Country 2]

ClientId，Country id，RegionId和LanguageId都应该是唯一的（包括空值是唯一的）。你使用

TOP 1

我还应该在你当前的代码中检查

TOP 1和TIES

，因为在不知道索引的情况下，它就不那么明显了。您可以使用具有相同排列的CASE语句（即，当ClientID=@@ClientID和CountryID=@@CountryID等时，第一个将是CASE语句。最后一个将有3个为null）。我认为你会有更好的表现，但我不确定。回答很好+1用于IIF的使用。我还没见过那个函数。这个查询的性能也比我的UNION语句好。我知道IIF函数，但我从来没有使用过它，因为我对case语句已经习以为常了。我真的应该开始使用它了。另外，与将空匹配与精确匹配分开一样，这使得它更易于维护+1感谢您的评论。1,2,4,8。。。在谈论优先事项时，技巧是一件容易记住的事情。如果您有两个优先级相同的项目，它甚至可以工作，并且很容易扩展或收回，因为这些数字只在计算中使用过。