查询索引中的碎片和重建SQL server索引
无论何时对基础数据执行插入、更新或删除操作，SQL Server
数据库引擎都会自动维护索引。随着时间的推移，这些修改可能会导致索引中的信息分散在数据库中（含有碎片）。当索引包含的页中的逻辑排序（基于键值）与数据文件中的物理排序不匹配时，就存在碎片。碎片非常多的索引可能会降低查询性能，导致应用程序响应缓慢。下面是一些简单的查询索引的sql。
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判断无用的索引：
[sql]
SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED
SELECT TOP 30
DB_NAME() AS DatabaseName ,
'[' + SCHEMA_NAME(o.Schema_ID) + ']' + '.' + '['
+ OBJECT_NAME(s.[object_id]) + ']' AS TableName ,
i.name AS IndexName ,
i.type AS IndexType ,
s.user_updates ,
s.system_seeks + s.system_scans + s.system_lookups AS [System_usage]
FROM sys.dm_db_index_usage_stats s
INNER JOIN sys.indexes i ON s.[object_id] = i.[object_id]
AND s.index_id = i.index_id
INNER JOIN sys.objects o ON i.object_id = O.object_id
WHERE s.database_id = DB_ID()
AND OBJECTPROPERTY(s.[object_id], 'IsMsShipped') = 0
AND s.user_seeks = 0
AND s.user_scans = 0
AND s.user_lookups = 0
AND i.name IS NOT NULL
ORDER BY s.user_updates DESC
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判断 哪些索引缺失：
[sql]
SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED
SELECT TOP 30
ROUND(s.avg_total_user_cost * s.avg_user_impact * ( s.user_seeks
+ s.user_scans ),
0) AS [Total Cost] ,
s.avg_total_user_cost * ( s.avg_user_impact / 100.0 ) * ( s.user_seeks
+ s.user_scans ) AS Improvement_Measure ,
DB_NAME() AS DatabaseName ,
d.[statement] AS [Table Name] ,
equality_columns ,
inequality_columns ,
included_columns
FROM sys.dm_db_missing_index_groups g
INNER JOIN sys.dm_db_missing_index_group_stats s ON s.group_handle = g.index_group_handle
INNER JOIN sys.dm_db_missing_index_details d ON d.index_handle = g.index_handle
WHERE s.avg_total_user_cost * ( s.avg_user_impact / 100.0 ) * ( s.user_seeks
+ s.user_scans ) > 10
ORDER BY [Total Cost] DESC ,
s.avg_total_user_cost * s.avg_user_impact * ( s.user_seeks
+ s.user_scans ) DESC
看看那些索引维护成本很高 通俗的说就是更新次数大于使用这个索引的次数
[sql]
SELECT TOP 20
DB_NAME() AS DatabaseName ,
'[' + SCHEMA_NAME(o.Schema_ID) + ']' + '.' + '['
+ OBJECT_NAME(s.[object_id]) + ']' AS TableName ,
i.name AS IndexName ,
i.type AS IndexType ,
( s.user_updates ) AS update_usage ,
( s.user_seeks + s.user_scans + s.user_lookups ) AS retrieva l_usage ,
( s.user_updates ) - ( s.user_seeks + user_scans + s.user_lookups ) AS maintenance_cost ,
s.system_seeks + s.system_scans + s.system_lookups AS system_usage ,
s.last_user_seek ,
s.last_user_scan ,
s.last_user_lookup
FROM sys.dm_db_index_usage_stats s
INNER JOIN sys.indexes i ON s.[object_id] = i.[object_id]
AND s.index_id = i.index_id
INNER JOIN sys.objects o ON i.object_id = O.object_id
WHERE s.database_id = DB_ID('{0}')
AND i.name IS NOT NULL
AND OBJECTPROPERTY(s.[object_id], 'IsMsShipped') = 0
AND ( s.user_seeks + s.user_scans + s.user_lookups ) > 0
ORDER BY maintenance_cost DESC
常常使用的索引查看 看看你常用使用的索