sqlserver 索引

SET STATISTICS io ON 
SET STATISTICS time ON 

-- 1. 没有索引(logical reads 568)
SELECT FirstName, LastName FROM dbo.Contact WHERE LastName LIKE ‘S%‘  

-- 创建非聚集索引
IF EXISTS (SELECT * FROM sys.indexes WHERE OBJECT_ID = OBJECT_ID(‘Person.Contact‘) AND name = ‘FullName‘) 
DROP INDEX Person.Contact.FullName; 
CREATE NONCLUSTERED INDEX FullName ON Person.Contact( LastName, FirstName ); 
GO 

-- 2. 完全覆盖的查询(logical reads 14)
SELECT FirstName, LastName FROM dbo.Contact WHERE LastName LIKE ‘S%‘   

-- 3. 非完全覆盖的查询(logical reads 568) SQL Server觉得使用索引查找，比直接扫描还要做更多的工作，因此没有使用索引.
SELECT * FROM dbo.Contact WHERE LastName LIKE ‘S%‘   

-- 4. 非完全覆盖的查询(logical reads 111) 改变where条件，从而减少查询结果的范围，增加使用索引的好处，SQL Server使用索引查找来缩短查询时间.
SELECT * FROM dbo.Contacts WHERE LastName LIKE ‘Ste%‘

CREATE CLUSTERED INDEX IX_SalesOrderDetail ON dbo.SalesOrderDetail (SalesOrderID, SalesOrderDetailID) 
GO 

-- 1. 堆表查询(logical reads 1495) & 聚集索引表查询(logical reads 3)
SELECT * FROM SalesOrderDetailWHERE SalesOrderID = 43671 AND SalesOrderDetailID = 120

-- 2. 堆表查询(logical reads 1495) & 聚集索引表查询(logical reads 1513)
--    ProductID列不是聚集索引的键。两种表都进行了表扫描。因为包含了聚集索引，聚集索引表更大，所以扫描了更多的次数。
SELECT * FROM SalesOrderDetail WHERE ProductID = 755

CREATE NONCLUSTERED INDEX FK_ProductID_ ModifiedDate 
       ON Sales.SalesOrderDetail (ProductID, ModifiedDate) 
       INCLUDE (OrderQty, UnitPrice, LineTotal) 

-- 该查询在包含列的非聚集索引下速度更快
SELECT ProductID , 
　　　　ModifiedDate , 
　　　　SUM(OrderQty) AS ‘No of Items‘ , 
　　　　AVG(UnitPrice) ‘Avg Price‘ , 
　　　　SUM(LineTotal) ‘Total Value‘ 
FROM Sales.SalesOrderDetail 
WHERE ProductID = 888 
GROUP BY ProductID ,ModifiedDate ;