Query regression by index or statistics?

  • Konstantin Reu

    Hall of Fame

    Points: 3149

    Here is article with exactly the same case study

    https://blogs.msdn.microsoft.com/psssql/2010/09/28/case-of-using-filtered-statistics/

    It does not have deep technical explanation, unfortunately. Respect to author of question.

    MS SQL 2008 MCITP x 3
    MS SQL 2012 MCSE x 2

  • TomThomson

    SSC Guru

    Points: 104772

    I very much liked this question.  Spent more than an hour thinking about what the optimser must be doing.  Once it clicked it was obvious, but it's a problem I'd never thought about before. 
    I will certainly be careful in future to look and see if I need to have filtered statistics in cases where the flat distribution assumption will cause misestimation that could lead to problem.  I guess the reaon I never thought about it before was that it had never caused performance issues that were as important as other performance issues (many of them not SQL).
    Thanks very much for the question.

    Tom

  • DamianC

    SSCertifiable

    Points: 7793

    Nice question, good explanation

    - Damian

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