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Replace the `MaterializedCte` and `MaterializedCteScan` extension nodes with the variants `LogicalPlan::MaterializedCte` and `LogicalPlan::MaterializedCteScan`. Each rule now states what it does with the nodes in its `match`, and the downcasts are removed from `PushDownFilter`, `PullUpCorrelatedExpr`, `head_output_expr` and the physical planner. `MaterializedCte::try_new` checks that the scans have the schema of the body, and `MaterializedCteScan::find_in` finds the scans of one CTE, also in subquery expressions. The unparser, the Substrait producer and the protobuf serializer return a "not implemented" error for the two variants. Plans and results do not change. Closes apache#26238. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
The body of a `MaterializedCte` kept all its columns, because each `MaterializedCteScan` was a leaf with the full schema of the body. A `MaterializedCteScan` now has a `projection`: the indexes of the columns of the body that it outputs. `OptimizeProjections` narrows each scan to the columns that its parent needs, as it does for a `TableScan`. At the `MaterializedCte` node it optimizes the continuation first, computes the union of the columns of all the scans of the CTE (also in subquery expressions and in the bodies of other CTEs), projects the body to this union, and gives each scan the new positions of its columns. `MaterializedCteScanExec` applies the projection to the shared buffered batches. The physical planner checks that each scan agrees with the schema of its body when it binds the scan. Closes apache#26240. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Which issue does this PR close?
Stacked on #26269. Only the last commit is new.
Rationale for this change
The body of a materialized CTE kept all its columns, also when no reference read them.
Before, all five columns were read and buffered:
After, only
aandbare read and buffered:What changes are included in this PR?
MaterializedCteScanhas a new fieldprojection: Option<Vec<usize>>: the indexes of the columns of the CTE body that the scan outputs.OptimizeProjectionsnarrows eachMaterializedCteScanto the columns that its parent needs, as it does for aTableScan.MaterializedCte,OptimizeProjectionsoptimizes the continuation first. It then computes the union of the columns of all the scans of the CTE, projects the body to this union, and gives each scan the new positions of its columns. Scans in subquery expressions and in the bodies of other CTEs are counted.MaterializedCteScanExecapplies the projection to the shared buffered batches.The projection in the scan makes the intermediate state (a narrow scan and a wide body) a valid plan, so no separate rule is necessary.
Notes:
SELECT count(*) FROM c) getsprojection=[]. If no reference reads a column, the body keeps its first column.DISTINCTor a recursive query are not removed.Comparison with PostgreSQL and DuckDB. This is what DuckDB does:
RemoveUnusedColumnsprunes the body to the columns that its references read (remove_unused_columns.cpp). PostgreSQL plans a CTE for full retrieval and does not prune (subselect.c).Are these changes tested?
Yes.
cte_materialized.slt:EXPLAINand result checks for the example above, a column that only a filter reads,count(*), a CTE that another CTE reads, references in subqueries, a volatile body, aDISTINCTbody, aliased columns, a self join, a recursive body and a CTE that nothing reads. Unit tests for the scan projection, nested CTEs, idempotence and the zero-column case.Are there any user-facing changes?
EXPLAINshowsprojection=[...]onMaterializedCteScanandMaterializedCteScanExecwhen the scan does not read all the columns.MaterializedCteScanhas the new public fieldprojection. The upgrade guide for 56.0.0 says this.