Atharv Rastogi created CALCITE-7916:
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Summary: RelMdPredicates should preserve input predicates through
Window
Key: CALCITE-7916
URL: https://issues.apache.org/jira/browse/CALCITE-7916
Project: Calcite
Issue Type: Bug
Reporter: Atharv Rastogi
{{RelMdPredicates}} currently has no {{getPredicates(Window,
RelMetadataQuery)}} handler. A {{Window}} therefore uses the generic
{{RelNode}} handler, which returns {{{}RelOptPredicateList.EMPTY{}}}, losing
facts already known about its input.
{{LogicalWindow}} preserves the input columns at their original positions and
appends the window-function results. Predicates already established on those
input columns therefore remain valid above the Window.
For example:
{{SELECT CASE WHEN deptno = 10 THEN rn ELSE -1 END AS result FROM ( SELECT
deptno, ROW_NUMBER() OVER (ORDER BY empno) AS rn FROM emp WHERE deptno = 10 )
ranked;}}
Once the window expression has been converted to a {{{}LogicalWindow{}}}, the
relevant plan shape is:
{{Project(result = CASE WHEN deptno = 10 THEN rn ELSE -1 END)
Window(rn = ROW_NUMBER() OVER (ORDER BY empno))
Filter(deptno = 10)
Scan(emp)}}
Every row entering and leaving the Window has {{{}deptno = 10{}}}. However,
querying the Window’s pulled-up predicates currently returns an empty list,
preventing consumers of this metadata from using that fact.
With the predicate preserved, the existing project expression-reduction rule
should be able to simplify the plan to:
{{Project(result = rn)
Window(rn = ROW_NUMBER() OVER (ORDER BY empno))
Filter(deptno = 10)
Scan(emp)}}
The same metadata can also expose redundant filters above a Window.
Proposed change:
Add a Window handler to {{RelMdPredicates}} that preserves the input’s
pulled-up predicates and their derived constant information. This applies to
constants, ranges, and other predicates on the unchanged input columns. It
should not infer new facts about the window-function results.
The returned metadata should contain the predicates applicable to the Window’s
output; join-specific {{leftInferredPredicates}} and
{{rightInferredPredicates}} from an input Join should not be carried over as
Window metadata.
Tests should cover constant and non-constant input predicates, nullable
columns, unchanged column positions, and expression simplification above a
Window.
Relevant source:
*
[RelMdPredicates.java|https://github.com/apache/calcite/blob/main/core/src/main/java/org/apache/calcite/rel/metadata/RelMdPredicates.java]:
missing Window handler and empty generic fallback.
*
[LogicalWindow.java|https://github.com/apache/calcite/blob/main/core/src/main/java/org/apache/calcite/rel/logical/LogicalWindow.java]:
output construction preserves input fields before appending window results.
*
[ReduceExpressionsRule.java|https://github.com/apache/calcite/blob/main/core/src/main/java/org/apache/calcite/rel/rules/ReduceExpressionsRule.java]:
Filter and Project reduction consume their input’s pulled-up predicates.
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