SQL INNER JOIN 与 Where Exists 性能考虑

Question

假设，我有一个从客户端发送的字符串列表，在这种情况下是区域。我有一个名为 Compliance Regions 的表。我想搜索具有名称属性和区域项的行应该存在于行上。

在 LINQ 中，我可以通过两种不同的方式来实现。如下所示，它们产生两个不同的 SQL 查询。 我的问题是我应该选择哪个？哪个查询的性能更好？

 List<string> regions = new List<string>() { "Canada", "EN 50530" };

           var cregions = from c in complianceRegions
                           from r in regions
                           where c.Name.Equals(r)
                           select c;

            var cregions2 = from c in complianceRegions
                            where regions.Any(x => x == c.Name)
                            select c;

生成的sql如下所示。

      -- cregions
   SELECT 
    [Extent1].[Id] AS [Id], 
    [Extent1].[Name] AS [Name], 
    [Extent1].[Description] AS [Description]
    FROM  [Administration].[ComplianceRegions] AS [Extent1]
    INNER JOIN  (SELECT 
        N'Canada' AS [C1]
        FROM  ( SELECT 1 AS X ) AS [SingleRowTable1]
    UNION ALL
        SELECT 
        N'EN 50530' AS [C1]
        FROM  ( SELECT 1 AS X ) AS [SingleRowTable2]) AS [UnionAll1] ON [Extent1].[Name] = [UnionAll1].[C1]  

和

--cregions2
    SELECT 
    [Extent1].[Id] AS [Id], 
    [Extent1].[Name] AS [Name], 
    [Extent1].[Description] AS [Description]
    FROM [Administration].[ComplianceRegions] AS [Extent1]
    WHERE  EXISTS (SELECT 
        1 AS [C1]
        FROM  (SELECT 
            N'Canada' AS [C1]
            FROM  ( SELECT 1 AS X ) AS [SingleRowTable1]
        UNION ALL
            SELECT 
            N'EN 50530' AS [C1]
            FROM  ( SELECT 1 AS X ) AS [SingleRowTable2]) AS [UnionAll1]
        WHERE [UnionAll1].[C1] = [Extent1].[Name]
    )

根据要求添加了执行计划。

Answer 1

鉴于这两种选择，第二种可能更好，因为列名上没有函数调用。

然而，两者并不相同。第一个进行部分匹配，第二个进行完全匹配。你真的应该做你想做的事。性能次于准确性。

两人都是痛苦的看着。类型转换 CHARINDEX() 的输出到索引？我们可以说“多余”吗？

他们提出了为什么查询不简单的问题:

select . . .
from [Administration].[ComplianceRegions] AS [Extent1]
where Extent1.Name in (N'Canada', N'EN 50530');

这是此逻辑的最简单且性能最佳的版本。