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