SQL Server Indexes


SQL Server Two Kinds Of Indexes Clustered Non-Clustered Clustered Indexes Require Data Table Physically Sorted Order Non Clustered Index Not Data Physically Sorted Enterprise Manager Create Index Wizard Index Fragmented SQL Server Indexes Introduction SQL Server Indexes


SQL Server Indexes


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"SQL Server Indexes

A database index is comparable to an index in a e book – it is comprised of a look up value, and a range identifier that corresponds to the row variety in a table. In SQL Server, there are two sorts of indexes – clustered and non-clustered. Clustered Indexes require that the statistics in the desk is bodily sorted in the order of the index. Because the information in a desk can be bodily sorted solely one way, there can be at most solely one clustered index per table. Non clustered index do now not require that statistics be bodily sorted, so there can be extra that one non-clustered index per table. In reality SQL Server lets in up to 249 non-clustered indexes per table. Because records is now not bodily sorted, vary searches the usage of a non clustered index are now not very efficient.


The command for developing an index in T-SQL is


CREATE [ UNIQUE ] [ CLUSTERED | NONCLUSTERED ] INDEX index_name ON { desk | view } ( column [ ASC | DESC ] [ ,...n ] ) [ WITH < index_option > [ ,...n] ] [ ON filegroup ] < index_option > :: = { PAD_INDEX | FILLFACTOR = fillfactor | IGNORE_DUP_KEY | DROP_EXISTING | STATISTICS_NORECOMPUTE | SORT_IN_TEMPDB }


PAD_INDEX specifies the proportion of area left free on the non-leaf stages of the index. FILLFACTOR specifies the proportion to fill the leaf pages. SORT_IN_TEMPDB specifies that intermediate consequences of the type will be saved in tempdb. This will increase disk house requirement however influences velocity index creation. STATISTICS_NO_RECOMPUTE tells the machine now not to mechanically replace index statistics.


Of course, indexes can additionally be created and managed the usage of the Enterprise Manager. They can be created the use of the Create Index Wizard, from the Database Diagram, or by way of enhancing fields in the Table Designer.


There is a change off with indexes.

 While they pace up execution of queries immensely, there is overhead related with them. They devour extra disk space, and require extra time to replace themselves on every occasion facts is up to date or appended to a table. When loading giant quantities of statistics it might also pay to drop the index prior to the loading, then recreate the index after the new information have been appended to the table. Indexes can be dropped the usage of the Table Designed, or through the usage of the DROP INDEX command.


Indexes can additionally emerge as fragmented. To defrag an index, both drop and recreate the index, or trouble the command dbcc indexdefrag




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