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Table scan cost %

  • February 23, 2008 at 6:13 am

    #74048

    Join made between Table A,B,C . based on one column i joined. logically i can join one column only. no issue in join. there is no index.

    but Table A & b goes table scan (cost = 0%) , estimated row count 3 lakhs for both, C Table has index scan row count is 4 lak.

    if table scan cost is zero mean anything harm ???

    Cost should be less for index and table scan ????

  • February 23, 2008 at 7:45 am

    #781354

    The cost % is the optimiser's estimate of how expensive an operation is relative to the rest of the query. If you have a table scan of a very small table and another operation (index seek or scan) on a very large table, it's quite normal that the table scan comes out with a low percentage.

    Gail Shaw
    Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
    SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

    We walk in the dark places no others will enter
    We stand on the bridge and no one may pass

  • February 26, 2008 at 10:06 am

    #782090

    Cost for indexed table is unnecessarily less than table scan if indexes are not created correctly.

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