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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