Question

我有一个名为ClientUrls的表，它具有以下结构：

+------------+----------------+----------+
| 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_GetClientUrls，它接受以下参数：

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

有关proc的信息

proc要求所有参数，并且它们都不是NULL
proc的目的是根据预定义的优先级返回表中的单个匹配行。优先级为ClientId＆gt;国家＆gt;区域＆gt;语言
ClientUrls表中的三个列可以为空。如果一列包含NULL，则它引用＆＃34; All＆＃34;。例如如果LanguageId为NULL，则它引用＆＃34; AllLanguages＆＃34;。因此，如果我们向proc发送一个5的LanguageId，我们首先查找，否则我们会尝试找到一个为NULL的。

优先级矩阵（1为第一个）

+---------+----------+-----------+----------+------------+
| Ranking | ClientId | CountryId | RegionId | LanguageId |
+---------+----------+-----------+----------+------------+
|       1 | NOT NULL | NOT NULL  | NOT NULL | NOT NULL   |
|       2 | NOT NULL | NULL      | NOT NULL | NOT NULL   |
|       3 | NOT NULL | NOT NULL  | NULL     | NOT NULL   |
|       4 | NOT NULL | NULL      | NULL     | NOT NULL   |
|       5 | NOT NULL | NOT NULL  | NOT NULL | NULL       |
|       6 | NOT NULL | NULL      | NOT NULL | NULL       |
|       7 | NOT NULL | NULL      | NULL     | NULL       |
+---------+----------+-----------+----------+------------+

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

预期回复（基于示例数据）

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

返回此行是因为NULL RegionId与正确的LanguageId匹配的优先级高于使用正确RegionId的NULL LanguageId匹配。

这是proc的代码（有效）。要真正回答我的问题，有没有更好的方法来写这个？如果我将来扩展这个表，我将继续增加UNION语句的数量，因此它不是真正可扩展的。

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

Answer 1

这很容易（如果我理解正确的话）。你可以用很少的代码完成它。此外，如果需要，它很容易扩展。

这是一个工作示例

--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

多数民众赞成。在旧版本的SQL中，您无法使用IIF，但如果需要，可以将其替换为case语句。

就像这样。

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，如果它不匹配则为0 通过累加总数，我们将始终选择最佳匹配组合。

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
+---------+----------+-----------+----------+------------+

我刚刚对此进行了更新，以确保您通过null选项获得非null版本。

如果您编辑结果以返回多于前1，您可以按正确的顺序查看项目。即如果你将语言从2改为1，你将得到1,1,1,1行超过1,1,1，Null选项

Answer 2

未经测试，但你可以这样做：

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

通过为每个匹配项赋值并选择最高值，您可以减少所需的代码。但是你会增加所需的案例陈述数量，而不是工会数量。

这也可以是函数而不是存储过程。因此，在其他查询中可以更容易地使用它

Answer 3

您可以将where子句更改为：

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

编码方式，它的代码更少。但调整问题更多。

Answer 4

另一种选择可能是尝试操纵NULL值来创建层次结构，如下所示：

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

存储过程以优先级基于可空列返回数据

4 个答案: