Question

我有一个画面生成的查询，如下所示：

SELECT (((DATEPART(year,(CASE
WHEN 0 = ISDATE(CAST([table1].[M_Date] AS VARCHAR)) THEN NULL
ELSE DATEADD(day, DATEDIFF(day, 0, CAST(CAST([table1].[M_Date] AS VARCHAR) as datetime)), 0) END)) * 10000) + (DATEPART(month,(CASE
WHEN 0 = ISDATE(CAST([table1].[M_Date] AS VARCHAR)) THEN NULL
ELSE DATEADD(day, DATEDIFF(day, 0, CAST(CAST([table1].[M_Date] AS VARCHAR) as datetime)), 0) END)) * 100)) + DATEPART(day,(CASE
WHEN 0 = ISDATE(CAST([table1].[M_Date] AS VARCHAR)) THEN NULL
ELSE DATEADD(day, DATEDIFF(day, 0, CAST(CAST([table1].[M_Date] AS VARCHAR) as datetime)), 0) END))) AS [md:M_Date:ok]
FROM [tbl].[table] [table1]
GROUP BY (((DATEPART(year,(CASE
WHEN 0 = ISDATE(CAST([table1].[M_Date] AS VARCHAR)) THEN NULL
ELSE DATEADD(day, DATEDIFF(day, 0, CAST(CAST([table1].[M_Date] AS VARCHAR) as datetime)), 0) END)) * 10000) + (DATEPART(month,(CASE
WHEN 0 = ISDATE(CAST([table1].[M_Date] AS VARCHAR)) THEN NULL
ELSE DATEADD(day, DATEDIFF(day, 0, CAST(CAST([table1].[M_Date] AS VARCHAR) as datetime)), 0) END)) * 100)) + DATEPART(day,(CASE
WHEN 0 = ISDATE(CAST([table1].[M_Date] AS VARCHAR)) THEN NULL
ELSE DATEADD(day, DATEDIFF(day, 0, CAST(CAST([table1].[M_Date] AS VARCHAR) as datetime)), 0) END)))

表＆＃39>表＆＃39;表＆＃39;有两个索引：

列[M_Date]，[Team]，[Player]，[Second]上的聚簇索引。
列[Player]，[M_Date]，[Team]

当我查看查询的执行计划时，它告诉我正在使用第二个索引。这对我来说似乎很奇怪，因为我认为只有当涉及的列形成索引的最左前缀时才能使用索引。（正如here所解释的）这个查询没有。如果有人能解释它是什么我不理解，或者如果这只是一个奇怪的情况下使用不正确的索引，你的帮助将不胜感激！

Tableau生成的查询未达到最佳表索引

0 个答案: