[jira] [Created] (IMPALA-8647) The cardinality associated with a SelectNode is 0 even if its child node has a non-zero cardinality

["Fang-Yu Rao (JIRA)" <ji...@apache.org>]

Fang-Yu Rao created IMPALA-8647:
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             Summary: The cardinality associated with a SelectNode is 0 even if its child node has a non-zero cardinality
                 Key: IMPALA-8647
                 URL: https://issues.apache.org/jira/browse/IMPALA-8647
             Project: IMPALA
          Issue Type: Bug
          Components: Frontend
            Reporter: Fang-Yu Rao


Consider the following nested SQL statement.
{code:java}
EXPLAIN SELECT *
FROM functional_parquet.alltypessmall WHERE 1 IN
(SELECT int_col FROM functional_parquet.alltypestiny LIMIT 1);
{code}
It seems that the cardinality of the SelectNode should be 1 instead of 0. Specifically, if we had executed
{code:java}
compute stats functional_parquet.alltypestiny{code}
before issuing this SQL statement at the very beginning, the returned cardinality of this SelectNode would be 1 instead of 0. Not very sure if this is a bug. It looks like the cardinality of a SelectNode depends on whether there is stats information associated with its child node. The cardinality of a SelectNode would still be 0 even if its child node (ExchangeNode in this case) has a non-zero cardinality.



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