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  • T-SQL Tuesday #86 My all-time favorite personal SQL Server Enhancement Request: Automatically maintained columns

    I have heard the name T-SQL Tuesday for (like,) ever; but I have always been so into my own bundle of insanity that never took the time to figure out what it is. This changes today because I read a blog on Adam Machanic's (@adammachanic) blog that outlined the rules (here) and I have been keen to get back to blogging regularly. When I saw what ...
    Posted to Louis Davidson (Weblog) by drsql on January 10, 2017
  • Incorrect Results Caused By Adding an Index

    It’s not often that a SQL Server bug really surprises me or makes me wonder how it was never spotted before, but this is one of those. To get right into it, say you have the following two tables: CREATE PARTITION FUNCTION PF (integer) AS RANGE RIGHT FOR VALUES (1000, 2000, 3000, 4000, 5000);   ...
    Posted to Page Free Space (Weblog) by Paul White on August 20, 2013
  • Incorrect Results with Indexed Views

    Summary: If you use MERGE, indexed views and foreign keys, your queries can return incorrect results. Microsoft have released a fix for incorrect results returned when querying an indexed view. The problem applies to: SQL Server 2012 SQL Server 2008 R2 SQL Server 2008 The Knowledge Base article does not go into much detail, or ...
    Posted to Page Free Space (Weblog) by Paul White on February 5, 2013
  • MERGE Bug with Filtered Indexes

    A MERGE statement can fail, and incorrectly report a unique key violation when: The target table uses a unique filtered index; and No key column of the filtered index is updated; and A column from the filtering condition is updated; and Transient key violations are possible Example Tables Say we have ...
    Posted to Page Free Space (Weblog) by Paul White on December 9, 2012
  • Cardinality Estimation Bug with Lookups

    Estimated row counts on key or RID lookups where a filtering predicate is applied can be wrong in SSMS execution plans.  This error does not affect the optimizer’s ultimate plan selection, but it does look odd.  There are other cases where estimated row counts are inconsistent (for defensible reasons) but the behaviour shown in this post ...
    Posted to Page Free Space (Weblog) by Paul White on October 15, 2012
  • An Interesting MERGE Bug

    Summary: Investigating an optimiser transformation that exposes a bug in SQL Server’s MERGE implementation. I came across a Connect item today (by fellow SQL Server Central member ‘ALZDBA’) describing how using a combination of relatively new features can produce incorrect results or even an access violation inside SQL Server. Reproducing the ...
    Posted to Page Free Space (Weblog) by Paul White on August 3, 2010
  • When GETDATE() is not a constant

    A short while ago I was collecting wait stat information at a client and ran across a very peculiar situation that I would like to share. Let me start by saying that for years I have coded with the understanding that when you include a system function in the SELECT list of a TSQL statement the function was evaluated once at the beginning and that ...
    Posted to Andrew Kelly (Weblog) by Andrew Kelly on February 27, 2008
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