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Posted to issues-all@impala.apache.org by "Aman Sinha (Jira)" <ji...@apache.org> on 2020/07/02 05:52:00 UTC

[jira] [Created] (IMPALA-9915) Num distinct values for IS [NOT] NULL predicate should be 2

Aman Sinha created IMPALA-9915:
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             Summary: Num distinct values for IS [NOT] NULL predicate should be 2
                 Key: IMPALA-9915
                 URL: https://issues.apache.org/jira/browse/IMPALA-9915
             Project: IMPALA
          Issue Type: Bug
          Components: Frontend
    Affects Versions: Impala 3.4.0
            Reporter: Aman Sinha


Currently, the NDV of all predicates is hardcoded to 3 following the 3-valued logic (True/False/Unknown). This is done in Predicate.analyzeImpl() method.  For IsNullPredicate which represents IS NULL and IS NOT NULL, strictly speaking the NDV should be 2 since it should only evaluate to True or False. Fixing this is more of a technicality and is not too consequential.  There are targeted tests in ExprCardinalityTest that should be updated when this is fixed.



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