SQL Server2008 Filtered Indexes
SQL Server Filtered Indexes - What They Are, How to Use and Performance Advantages
Written By: Arshad Ali -- 7/2/2009 -
Problem
SQL Server 2008 introduces Filtered Indexes which is an index with a WHERE clause. Doesn’t it sound awesome especially for a table that has huge amount of data and you often select only a subset of that data? For example, you have a lot of NULL values in a column and you want to retrieve records with only non-NULL values (in SQL Server 2008, this is called Sparse Column). Or in another scenario you have several categories of data in a particular column, but you often retrieve data only for a particular category value.
In this tip, I am going to walk through what a Filtered Index is, how it differs from other indexes, its usage scenario, its benefits and limitations.
Solution
A Filtered Index, which is an optimized non-clustered index, allows us to define a filter predicate, a WHERE clause, while creating the index. The B-Tree containing rows from the filtered index will contain only those rows which satisfy the filter criteria used while creating the index. This optimized index offers several benefits over a full table non-clustered index as follows:
As discussed above, the filtered index contains only those rows which satisfy the defined filter criteria. As a result it reduces the storage space requirement for the index. In the example below I will explain it more.
The filtered statistics or statistics for a filtered index are more compact and accurate, because they consider only the rows in the filtered index and the smaller size of the filtered index reduces the cost/overhead of updating the statistics.
The impact of data modification is less with a filtered index as it is updated only when the data of the index is impacted or a new record is inserted matching the filter criteria.
Maintenance costs will be reduced as well since only a subset of rows will be in consideration while re-organizing or rebuilding the index
Ïà¹ØÎĵµ£º
Sql´úÂë
--²ÉÓÃSQLÓï¾äʵÏÖsql2005ºÍExcel Êý¾ÝÖ®¼äµÄÊý¾Ýµ¼Èëµ¼³ö£¬ÔÚÍøÉÏÕÒÀ´Ò»--Ï£¬ÊµÏÖ·½·¨ÊÇÕâÑùµÄ£º
--Excel---->SQL2005 µ¼È룺
select * into useinfo from O ......
1 £¬¶ÔÓÚÈÕÆÚ×Ö¶Î×Ö¶Î
access±íʾΪ£º#1981-28-12#
SQLSERVER2000±íʾΪ£º''1981-02-12''
2,SQLÓï¾äÇø±ð£¬select ,update ÔÚ¶Ôµ¥±í²Ù×÷ʱ¶¼²î²»¶à£¬
µ«¶à±í²Ù×÷ʱupdateÓï¾äµÄÇø±ðACCESSÓëSQLSERVERÖеÄUpdateÓï¾ä¶Ô±È:
SQLSERVERÖиüжà±íµÄUpdateÓï¾ä:
Update Tab1
SET a.Name = b.Name
from Tab1 a,Tab2 b
Whe ......
SQLµÄÓÅ»¯Ó¦¸Ã´Ó5¸ö·½Ãæ½øÐе÷Õû£º
1.È¥µô²»±ØÒªµÄ´óÐͱíµÄÈ«±íɨÃè
2.»º´æÐ¡ÐͱíµÄÈ«±íɨÃè
3.¼ìÑéÓÅ»¯Ë÷ÒýµÄʹÓÃ
4.¼ìÑéÓÅ»¯µÄÁ¬½Ó¼¼Êõ
5.¾¡¿ÉÄܼõÉÙÖ´Ðмƻ®µÄCost
SQLÓï¾ä£º
ÊǶÔÊý¾Ý¿â(Êý¾Ý)½øÐвÙ×÷µÄΩһ;¾¶£»
ÏûºÄÁË70%~90%µÄÊý¾Ý¿â×ÊÔ´£»¶ÀÁ¢ÓÚ³ÌÐòÉè¼ÆÂß¼£¬Ïà¶ÔÓÚ¶Ô³ÌÐòÔ´´úÂëµÄÓÅ»¯£¬¶ÔSQLÓï¾äµÄÓÅ» ......
Ò»£ºSQL Loader µÄÌØµã
oracle×Ô¼º´øÁ˺ܶàµÄ¹¤¾ß¿ÉÒÔÓÃÀ´½øÐÐÊý¾ÝµÄÇ¨ÒÆ¡¢±¸·ÝºÍ»Ö¸´µÈ¹¤×÷¡£µ«ÊÇÿ¸ö¹¤¾ß¶¼ÓÐ×Ô¼ºµÄÌØµã¡£
±ÈÈç˵expºÍimp¿ÉÒÔ¶ÔÊý¾Ý¿âÖеÄÊý¾Ý½øÐе¼³öºÍµ¼³öµÄ¹¤×÷£¬ÊÇÒ»ÖֺܺõÄÊý¾Ý¿â±¸·ÝºÍ»Ö¸´µÄ¹¤¾ß£¬Òò´ËÖ÷ÒªÓÃÔÚÊý¾Ý¿âµÄÈȱ¸·ÝºÍ»Ö¸´·½Ãæ¡£ÓÐ×ÅËٶȿ죬ʹÓüòµ¥£¬¿ì½ÝµÄÓŵ㣻ͬʱҲÓÐһЩȱµ ......