Re: Hash Anti Join Requirements

> working with some folks who are frightened by anti-joins

Last Halloween I went as an anti-join. It was pretty scary.

Harrison:

"Performance from the hash antijoin was dramatically better than for any other [anti-join optimization] method we tried.

...

To take advantage of Oracle's antijoin optimizations, the following must be true:

• CBO optimization must be enabled
• Antijoin columns must not be NULL, because of the table definition or a not null clause in the SQL
• The subquery is not correlated
• The parent query does not contain an OR clause
• The db parm ALWAYS_ANTI_JOIN is set to MERGE or HASH, or a MERGE_AJ or HASH_AJ hint is in the subquery"

-- 
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-- 
Author: Greg Moore
  INET: sqlgreg_at_pacbell.net

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