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Table Scan or Clustered Index scan

  • May 22, 2006 at 4:09 am

    #112920

    Hi,

     

    Which is best Table Scan or Clustered Index scan..?? I know clustered Index is best. But the Execution plan result and STATISTICS IO making me to believe Table scan is best...

    I have a table with out clustered index. When i execute a simple select on that table

     

    select * from table_x

     

    it uses table scan.The overall select cost is 0.436

     

    STATISTICS IO

    ==================

    Scan count 1, logical reads 553, physical reads 0, read-ahead reads 72.

     

    same table with clustered index

     

    select cost: 2.33

    STATISTICS IO

    ==================

     Scan count 1, logical reads 3008, physical reads 0, read-ahead reads 0.

     

    if you see the logical read, its much much high with clustered index

     

    Please Help me

     

    Thanks

    Blackangel

  • May 22, 2006 at 6:51 am

    #639216

    A clustered index scan is a table scan. If you put  a clustered index on a table you will never actually see a table scan.

    All that happens is that it goes straight to the leaf level of the indexe and scans it and since the leaf level of a clustered index contains the actual data for the table its just the same.

    But to make any use of an index you need to include a where clause that would elimate some of the rows and for which a suitable index existed.

    hth

    David

     

     

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