SQL：使用冗余联合代码优化嵌套查询？

尽管下面的查询对于我的使用效果非常好，但我试图了解是否有优化的方法，因为它在UNION的两个语句中使用相同的嵌套子查询。我的直觉告诉我，应该有一种方法来查找子查询一次，并对联合的两个部分使用该结果，但我在试图跨联合使用join时遇到了语法问题

SELECT ClientLocalName, ClientLocalID, ClientMasterID, 1 HierarchyType
    FROM dbo.ClientLocal
    WHERE clientLocalID = 
        ANY (SELECT HierarchyItem FROM dbo.ClientPhone WHERE PhoneNumber LIKE '%0123456789')
UNION
SELECT ClientMasterName, '0', clientMasterID, 2
    FROM dbo.ClientMaster
    WHERE clientMasterID = 
        ANY (SELECT HierarchyItem FROM dbo.ClientPhone WHERE PhoneNumber LIKE '%0123456789')
ORDER BY HierarchyType ASC;

为了帮助解释为什么需要原始查询，想象一下本地客户机和主客户机的概念——本地客户机与主客户机绑定，但主客户机可能有也可能没有任何本地客户机。同样，与每个客户端关联的电话号码只应绑定到本地客户端或主客户端，因此在第二条语句中，本地客户端ID的“0”是硬编码的，因为没有关联

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顺便说一下，这将针对Microsoft SQL Server 2008 R2运行。

如果您不喜欢重复代码，可以使用公共表表达式：

WITH cte AS (
  SELECT HierarchyItem FROM dbo.ClientPhone WHERE PhoneNumber LIKE '%0123456789'
)
SELECT ClientLocalName, ClientLocalID, ClientMasterID, 1 HierarchyType
FROM dbo.ClientLocal
WHERE clientLocalID IN (SELECT HierarchyItem FROM cte)
UNION
SELECT ClientMasterName, '0', clientMasterID, 2
FROM dbo.ClientMaster
WHERE clientMasterID IN (SELECT HierarchyItem FROM cte)
ORDER BY HierarchyType ASC;

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我能看到的唯一明显的优化是使用union all而不是union：

由于最后一列的原因，子选择之间显然没有重复项。这假定在每个子选择中都没有重复项

我不知道SQL Server对=ANY的处理方式，但我假设它与中的基本相同。=ANY子查询将为每个子查询运行一次，但第二次将缓存结果。您可以将其简化为：

SELECT ClientLocalName, ClientLocalID, ClientMasterID, 1 HierarchyType
FROM ((SELECT ClientLocalName, ClientLocalID, ClientMasterID
       FROM dbo.ClientLocal
      ) UNION ALL
      (SELECT ClientLocalName, '0', ClientMasterID
       FROM dbo.ClientMasterName
      ) 
     ) c        
WHERE c.clientLocalID = ANY (SELECT HierarchyItem FROM dbo.ClientPhone WHERE PhoneNumber LIKE '%0123456789')
ORDER BY HierarchyType ASC;

我不知道这是否会有很大的改善

---

LIKE模式在数字的开头有一个通配符，这使得它很难优化。

因为似乎没有人提到它：代码更少并不一定意味着它的执行速度也会更快。人们常常认为CTE是首先执行的，或者是在有多个CTE的情况下按顺序执行，然后应用最终的查询；事实并非如此。事实上，服务器将处理cte，就像它是FROM或JOIN子句中的某个派生表一样，因此选择完全相同的查询计划来执行它们。为了避免系统必须像“%0123…”一样扫描ClientPhone表两次，这是一个非常“烦人”的操作，您必须先扫描一次，然后将结果存储在临时表中，然后在实际查询中使用所述临时表

为了提供一些上下文，我冒昧地创建了一些示例数据，请参见下面的代码。我的测试结果是：

原始查询需要71毫秒 CTE版本需要71毫秒，并使用完全相同的查询计划 创建临时表需要26毫秒，使用它的查询需要23毫秒 因此，即使服务器需要创建临时表并填充它，合并后的临时表仍然只需要49毫秒，而不是原来的71毫秒

当然，根据涉及的记录数量和重复查询的复杂性，您的里程数可能会有所不同，正如我所说的，像“%blah”这样的重复查询是一件令人讨厌的事情，因为它需要对表进行完整扫描，或者需要一点覆盖索引。如果是在pk_field=@value的位置，效果可能会非常不同

快乐的询问

IF DB_ID('test') IS NULL CREATE DATABASE test
GO
USE test
GO

-- setup
IF OBJECT_ID('ClientPhone') IS NOT NULL DROP TABLE ClientPhone 
IF OBJECT_ID('ClientLocal') IS NOT NULL DROP TABLE ClientLocal
IF OBJECT_ID('ClientMaster') IS NOT NULL DROP TABLE ClientMaster
GO
SELECT TOP 50000 
       HierarchyItem = IDENTITY(int, 1, 1),
       PhoneNumber   = Convert(varchar(100), NewID())
  INTO dbo.ClientPhone 
  FROM sys.objects x1, sys.columns x2, sys.objects x3, sys.columns x4

SELECT ClientLocalName = 'client dummy', 
       ClientLocalID   = Convert(int, Rand(HierarchyItem * 37) * 50000), 
       ClientMasterID   = Convert(int, Rand(HierarchyItem * 47) * 50000), 
       HierarchyType   = 1
  INTO dbo.ClientLocal
  FROM dbo.ClientPhone 

SELECT ClientMasterName = 'master dummy', 
       ClientLocalID    = Convert(int, Rand(HierarchyItem * 51) * 50000), 
       ClientMasterID   = Convert(int, Rand(HierarchyItem * 53) * 50000), 
       HierarchyType    = 2
  INTO dbo.ClientMaster
  FROM dbo.ClientPhone 

GO
-- original 
SELECT ClientLocalName, ClientLocalID, ClientMasterID, 1 HierarchyType
  FROM dbo.ClientLocal
 WHERE ClientLocalID = ANY (SELECT HierarchyItem FROM dbo.ClientPhone WHERE PhoneNumber LIKE '%01')
UNION
SELECT ClientMasterName, '0', ClientMasterID, 2
  FROM dbo.ClientMaster
 WHERE ClientMasterID = ANY (SELECT HierarchyItem FROM dbo.ClientPhone WHERE PhoneNumber LIKE '%01')
ORDER BY HierarchyType ASC;

-- CTE
;WITH cte
   AS (SELECT HierarchyItem FROM dbo.ClientPhone WHERE PhoneNumber LIKE '%01')

SELECT ClientLocalName, ClientLocalID, ClientMasterID, 1 HierarchyType
  FROM dbo.ClientLocal
 WHERE ClientLocalID = ANY (SELECT HierarchyItem FROM cte)
UNION
SELECT ClientMasterName, '0', ClientMasterID, 2
  FROM dbo.ClientMaster
 WHERE ClientMasterID = ANY (SELECT HierarchyItem FROM cte)
ORDER BY HierarchyType ASC;

-- temp table
IF OBJECT_ID('tempdb..#ClientPhone') IS NOT NULL DROP TABLE #ClientPhone

SELECT HierarchyItem INTO #ClientPhone FROM dbo.ClientPhone WHERE PhoneNumber LIKE '%01'

SELECT ClientLocalName, ClientLocalID, ClientMasterID, 1 HierarchyType
  FROM dbo.ClientLocal
 WHERE ClientLocalID = ANY (SELECT HierarchyItem FROM #ClientPhone)
UNION
SELECT ClientMasterName, '0', ClientMasterID, 2
  FROM dbo.ClientMaster
 WHERE ClientMasterID = ANY (SELECT HierarchyItem FROM #ClientPhone)
ORDER BY HierarchyType ASC;

---

仅仅因为您重复了代码，并不一定意味着它会被重复计算。优化器很可能会发现这是重复的，并重用第一次评估的结果。除非如此，否则重新评估似乎更为合适。如果只是重复代码，请使用提供的CTE解决方案。此查询中可能有很多地方需要优化。首先，我不知道该查询如何运行，因为除非这些列具有相同的名称，否则不能合并ClientLocalName和ClientMasterName。你能提供一点样本数据和你的预期结果吗？ClientPhone的CTE可以工作，但这实际上就是您要获取的数据吗？@Shawn只要数据类型在各个联合中相同，列的名称就无关紧要。这个查询确实工作得很好。无论如何，卢卡斯的回答提供了我想要的。@stickybit是正确的，但真正的代码在重复的代码中会有更多的条件，因此这里有一个很好的动机来避免重复。@stickybit:事实上，重复的代码肯定会被计算多次。当然，基本数据只需要加载到缓存中一次，但实际执行的频率与要求的频率相同。请参阅下面的示例。值得一提的是，将UNION更改为UNION ALL可以更改总体结果，如果子结果中存在重复项，则选择作为UNION或UNION ALL的操作数。列ClientLocalID和ClientMasterID的命名表明，子结果中存在PK，因此不会出现重复。但是，如果这是一个错误的印象，则在使用UNION ALL时，需要使用SELECT DISTINCT使子结果自己不重复，这可能会更快，因为重复数据消除的集合更小。不幸的是，基本的

SELECT ClientLocalName, ClientLocalID, ClientMasterID, 1 HierarchyType
FROM ((SELECT ClientLocalName, ClientLocalID, ClientMasterID
       FROM dbo.ClientLocal
      ) UNION ALL
      (SELECT ClientLocalName, '0', ClientMasterID
       FROM dbo.ClientMasterName
      ) 
     ) c        
WHERE c.clientLocalID = ANY (SELECT HierarchyItem FROM dbo.ClientPhone WHERE PhoneNumber LIKE '%0123456789')
ORDER BY HierarchyType ASC;

IF DB_ID('test') IS NULL CREATE DATABASE test
GO
USE test
GO

-- setup
IF OBJECT_ID('ClientPhone') IS NOT NULL DROP TABLE ClientPhone 
IF OBJECT_ID('ClientLocal') IS NOT NULL DROP TABLE ClientLocal
IF OBJECT_ID('ClientMaster') IS NOT NULL DROP TABLE ClientMaster
GO
SELECT TOP 50000 
       HierarchyItem = IDENTITY(int, 1, 1),
       PhoneNumber   = Convert(varchar(100), NewID())
  INTO dbo.ClientPhone 
  FROM sys.objects x1, sys.columns x2, sys.objects x3, sys.columns x4

SELECT ClientLocalName = 'client dummy', 
       ClientLocalID   = Convert(int, Rand(HierarchyItem * 37) * 50000), 
       ClientMasterID   = Convert(int, Rand(HierarchyItem * 47) * 50000), 
       HierarchyType   = 1
  INTO dbo.ClientLocal
  FROM dbo.ClientPhone 

SELECT ClientMasterName = 'master dummy', 
       ClientLocalID    = Convert(int, Rand(HierarchyItem * 51) * 50000), 
       ClientMasterID   = Convert(int, Rand(HierarchyItem * 53) * 50000), 
       HierarchyType    = 2
  INTO dbo.ClientMaster
  FROM dbo.ClientPhone 

GO
-- original 
SELECT ClientLocalName, ClientLocalID, ClientMasterID, 1 HierarchyType
  FROM dbo.ClientLocal
 WHERE ClientLocalID = ANY (SELECT HierarchyItem FROM dbo.ClientPhone WHERE PhoneNumber LIKE '%01')
UNION
SELECT ClientMasterName, '0', ClientMasterID, 2
  FROM dbo.ClientMaster
 WHERE ClientMasterID = ANY (SELECT HierarchyItem FROM dbo.ClientPhone WHERE PhoneNumber LIKE '%01')
ORDER BY HierarchyType ASC;

-- CTE
;WITH cte
   AS (SELECT HierarchyItem FROM dbo.ClientPhone WHERE PhoneNumber LIKE '%01')

SELECT ClientLocalName, ClientLocalID, ClientMasterID, 1 HierarchyType
  FROM dbo.ClientLocal
 WHERE ClientLocalID = ANY (SELECT HierarchyItem FROM cte)
UNION
SELECT ClientMasterName, '0', ClientMasterID, 2
  FROM dbo.ClientMaster
 WHERE ClientMasterID = ANY (SELECT HierarchyItem FROM cte)
ORDER BY HierarchyType ASC;

-- temp table
IF OBJECT_ID('tempdb..#ClientPhone') IS NOT NULL DROP TABLE #ClientPhone

SELECT HierarchyItem INTO #ClientPhone FROM dbo.ClientPhone WHERE PhoneNumber LIKE '%01'

SELECT ClientLocalName, ClientLocalID, ClientMasterID, 1 HierarchyType
  FROM dbo.ClientLocal
 WHERE ClientLocalID = ANY (SELECT HierarchyItem FROM #ClientPhone)
UNION
SELECT ClientMasterName, '0', ClientMasterID, 2
  FROM dbo.ClientMaster
 WHERE ClientMasterID = ANY (SELECT HierarchyItem FROM #ClientPhone)
ORDER BY HierarchyType ASC;