在 WHERE 子句中使用 CASE 或 AND/OR 来限制结果答案

【问题标题】：Use CASE or AND/OR in WHERE Clause To Limit Results在 WHERE 子句中使用 CASE 或 AND/OR 来限制结果
【发布时间】：2021-05-02 22:11:10
【问题描述】：

我知道有很多类似的问题，我经历了大约 20 个问题来寻找答案。大多数设置单个变量，或使用我目前拥有的 AND/OR 格式。

我正在尝试创建一个函数，在其中传递城市、州、邮编和国家/地区的组合，它会定位并返回所有信息。如果我使用 OR 方法，如果 Zip 和 Country 不为 NULL，则第一个选项将返回结果，但是只有 Zip 不为 NULL 的选项也可以返回结果。这些是我希望它们评估的顺序（从上到下）。我只重调了一个值，但我不能保证结果的顺序相同，所以我想消除冗余结果。

这是我当前的查询：

SELECT TOP(1) City, State_abbr, State_long, Zip, Country, County, Longitude, Latitude
      FROM [ULTRA].[dbo].[CityStateInfo]
      WHERE
        (   -- Zip Code, Country: Will find City and State  /* BEST RESULTS */
            @inZip IS NOT NULL AND 
            @inCountry IS NOT NULL 
            AND 
            Zip = @inZip AND 
            Country = @inCountry 
        )
        OR
        (   -- City, State, Country:  Will find first Zip Code in City, State
            @inCity IS NOT NULL AND 
            @inState IS NOT NULL AND 
            @inCountry IS NOT NULL 
            AND 
            City = @inCity AND 
            (State_abbr = @inState OR State_long = @inState) AND 
            Country = @inCountry 
        )
        OR
        (   -- City, State: Will find first Zip Code in City, State. Will find Country
            @inCity IS NOT NULL AND 
            @inState IS NOT NULL 
            AND 
            City = @inCity AND 
            (State_abbr = @inState OR State_long = @inState) 
        )
        OR          
        (   -- City, State, Zip: Will find Country
            @inState IS NOT NULL AND 
            @inCountry IS NOT NULL 
            AND 
            (State_abbr = @inState AND State_long = @inState) AND 
            Country = @inCountry 
        )
        OR
        (   -- City, Zip:  Will find State and Country
            @inCity IS NOT NULL AND 
            @inState IS NOT NULL 
            AND 
            City = @inCity AND 
            (State_abbr = @inState AND State_long = @inState) 
        )
        OR
        (   -- State, Zip:  Will find City and Country
            @inCity IS NOT NULL AND 
            @inCountry IS NOT NULL 
            AND 
            City = @inCity AND 
            Country = @inCountry 
        )
        OR
        (
            -- Zip Code: Will find City, State and Country  ** Possible error if Country is not US or Canada
            @inZip IS NOT NULL 
            AND 
            Zip = @inZip 
        )

这就是我用 CASE 尝试过的

SELECT TOP(1) City, State_abbr, State_long, Zip, Country, County, Longitude, Latitude
      FROM [ULTRA].[dbo].[CityStateInfo]
      WHERE
        CASE
            -- Zip Code, Country: Will find City and State  /* BEST RESULTS */
            WHEN ( @inZip IS NOT NULL AND @inCountry IS NOT NULL )
                THEN Zip = @inZip AND Country = @inCountry 

            -- City, State, Country:  Will find first Zip Code in City, State
            WHEN ( @inCity IS NOT NULL AND @inState IS NOT NULL AND @inCountry IS NOT NULL )
                THEN City = @inCity AND (State_abbr = @inState OR State_long = @inState) AND Country = @inCountry 
        END

我收到了

“=”附近的语法不正确。

对应于= in "THEN Zip = @inZip AND Country = @inCountry。

如果无法使用 CASE，是否可以对我的 OR 语句做一些不同的事情来实现我正在寻找的东西？

MS SQL Server v15.0.2070
SSMS v18.5

【问题讨论】：

另一种方法是根据应用程序（.net 或其他）中的值构建查询，并将准备好的带有简单条件的查询发送到 sql 服务器。请注意，OR 查询的性能很差。
如果性能不好，甚至可以使用动态 SQL。
@DaleK 我喜欢动态 SQL 的想法。我试过了，但在声明变量时遇到了一个奇怪的错误。
那将是一个单独的问题。由于这个问题有答案，您应该看看它是否解决了所提出的问题，如果是，请接受它。
您可以在where 子句中使用case，就像this 答案中所示的on 子句一样。性能可能会受到影响，但使用 recompile 提示可能会有所帮助。

标签： sql sql-server tsql case

【解决方案1】：

我们可以对每组条件做一个UNION ALL，添加一个排序列并取第一个。

这应该非常高效，因为它使用MERGE CONCATENATION，如Paul White describes：

SELECT TOP(1) City, State_abbr, State_long, Zip, Country, County, Longitude, Latitude
    (SELECT TOP(1) 1 AS Ordering, City, State_abbr, State_long, Zip, Country, County, Longitude, Latitude
      FROM [ULTRA].[dbo].[CityStateInfo]
      WHERE
        (   -- Zip Code, Country: Will find City and State  /* BEST RESULTS */
            @inZip IS NOT NULL AND 
            @inCountry IS NOT NULL 
            AND 
            Zip = @inZip AND 
            Country = @inCountry 
        )
    UNION ALL
    SELECT TOP(1) 2, City, State_abbr, State_long, Zip, Country, County, Longitude, Latitude
      FROM [ULTRA].[dbo].[CityStateInfo]
      WHERE
        (   -- City, State, Country:  Will find first Zip Code in City, State
            @inCity IS NOT NULL AND 
            @inState IS NOT NULL AND 
            @inCountry IS NOT NULL 
            AND 
            City = @inCity AND 
            (State_abbr = @inState OR State_long = @inState) AND 
            Country = @inCountry 
        )
    UNION ALL
    SELECT TOP(1) 3, City, State_abbr, State_long, Zip, Country, County, Longitude, Latitude
      FROM [ULTRA].[dbo].[CityStateInfo]
      WHERE
        (   -- City, State: Will find first Zip Code in City, State. Will find Country
            @inCity IS NOT NULL AND 
            @inState IS NOT NULL 
            AND 
            City = @inCity AND 
            (State_abbr = @inState OR State_long = @inState) 
        )
    UNION ALL
    SELECT TOP(1) 4, City, State_abbr, State_long, Zip, Country, County, Longitude, Latitude
      FROM [ULTRA].[dbo].[CityStateInfo]
      WHERE
        (   -- City, State, Zip: Will find Country
            @inState IS NOT NULL AND 
            @inCountry IS NOT NULL 
            AND 
            (State_abbr = @inState AND State_long = @inState) AND 
            Country = @inCountry 
        )
    UNION ALL
    SELECT TOP(1) 5, City, State_abbr, State_long, Zip, Country, County, Longitude, Latitude
      FROM [ULTRA].[dbo].[CityStateInfo]
      WHERE
        (   -- City, Zip:  Will find State and Country
            @inCity IS NOT NULL AND 
            @inState IS NOT NULL 
            AND 
            City = @inCity AND 
            (State_abbr = @inState AND State_long = @inState) 
        )
    UNION ALL
    SELECT TOP(1) 6, City, State_abbr, State_long, Zip, Country, County, Longitude, Latitude
      FROM [ULTRA].[dbo].[CityStateInfo]
      WHERE
        (   -- State, Zip:  Will find City and Country
            @inCity IS NOT NULL AND 
            @inCountry IS NOT NULL 
            AND 
            City = @inCity AND 
            Country = @inCountry 
        )
    UNION ALL
    SELECT TOP(1) 7, City, State_abbr, State_long, Zip, Country, County, Longitude, Latitude
      FROM [ULTRA].[dbo].[CityStateInfo]
      WHERE
        (
            -- Zip Code: Will find City, State and Country  ** Possible error if Country is not US or Canada
            @inZip IS NOT NULL 
            AND 
            Zip = @inZip 
        )
) t
ORDER BY ordering;

【讨论】：

【解决方案2】：

根据您的 CASE 示例，我猜您正在追求这样的事情（？）：

SELECT TOP(1) City, State_abbr, State_long, Zip, Country, County, Longitude, Latitude
      FROM [ULTRA].[dbo].[CityStateInfo]
      WHERE
        1 = CASE
                -- Zip Code, Country: Will find City and State  /* BEST RESULTS */
                WHEN ( @inZip IS NOT NULL AND @inCountry IS NOT NULL )
                    THEN 
                        CASE WHEN Zip = @inZip AND Country = @inCountry THEN 1 ELSE 0 END

                -- City, State, Country:  Will find first Zip Code in City, State
                WHEN ( @inCity IS NOT NULL AND @inState IS NOT NULL AND @inCountry IS NOT NULL )
                    THEN 
                        CASE WHEN City = @inCity AND (State_abbr = @inState OR State_long = @inState) AND Country = @inCountry 
                            THEN 1 ELSE 0 END
                ELSE 0          
            END

请注意，“ELSE 0”部分是可选的，如果您愿意，可以将其删除，因为如果 CASE 不匹配任何条件并一直到最后，它将返回 NULL，它永远不会等于 1。

【讨论】：

这种方法的问题是你几乎肯定会失去 sargability。

【解决方案3】：

为了确保该行只返回一次，添加额外的逻辑以确保它在已经找到时被忽略，例如替换

(
    -- Zip Code: Will find City, State and Country  ** Possible error if Country is not US or Canada
    @inZip IS NOT NULL 
    AND Zip = @inZip 
)

与

(
    -- Zip Code: Will find City, State and Country  ** Possible error if Country is not US or Canada
    @inZip IS NOT NULL 
    -- Only go through this branch if country is null because otherwise we have handled it elsewhere
    AND @inCountry IS NULL 
    AND Zip = @inZip 
)

并使用类似的逻辑来处理其他类似的情况。

【讨论】：

这可行，但我需要添加更多选项，因为我现在对变量非常具体。