[jira] [Created] (CALCITE-5117) Optimize the EXISTS sub-query by Metadata RowCount

["xiong duan (Jira)" <ji...@apache.org>]

xiong duan created CALCITE-5117:
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             Summary: Optimize the EXISTS sub-query by Metadata RowCount
                 Key: CALCITE-5117
                 URL: https://issues.apache.org/jira/browse/CALCITE-5117
             Project: Calcite
          Issue Type: Bug
          Components: core
    Affects Versions: 1.30.0
            Reporter: xiong duan


As same as the UNIQUE sub-query, before we convert the sub-query to RelNode. we use the Metadata to optimize it.

EXISTS sub-query, If the sub-query is guaranteed to produce at least one row, just return TRUE. If the sub-query is guaranteed to produce no row, just return FALSE.

For example:
{code:java}
select *
from dept as d
where EXISTS (select count(*) from emp e where d.deptno = e.deptno){code}
We can optimize it to:
{code:java}
EnumerableTableScan(table=[[scott, DEPT]]){code}



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