Home Forums Article Discussions Article Discussions by Author Discuss Content Posted by Gregory Larsen Stairway to T-SQL Part 2: Beyond T-SQL Basics: Level 3: Building a Correlated Subquery RE: Stairway to T-SQL Part 2: Beyond T-SQL Basics: Level 3: Building a Correlated Subquery

  • March 19, 2015 at 10:35 am

    #1785149

    Dennis Wagner-347763 (3/6/2014)

    The correlated subquery may be executed many times. It will be run once for each candidate row selected in the outer query.

    I believe that Jeff Moden refers to this as RBAR (row by agonizing row).

    Except that correlated subqueries *don't* run once per row of the outer query. It's an old and persistent myth that they do that.

    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

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