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Wiki / Plan Nodes / Scan

Subquery Scan

SubqueryScan

Scans the output of a subquery plan.

Reading PostgreSQL 18.6.

Description

Scans the output of a subquery plan.

Core node tag
T_SubqueryScan
Structured EXPLAIN Node Type
Subquery Scan
Inputs
A subquery child plan
Output
Subquery result tuples
Executor initializer
ExecInitSubqueryScan
Memory mechanism
unclassified

EXPLAIN names and attributes

Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.

Text names recorded by this source: Subquery Scan.

Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node.

Memory and temporary storage

This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.

Parallel execution and instrumentation

The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.

Callbacks in this build: none extracted from this node implementation.

Executor implementation notes

nodeSubqueryscan.c Support routines for scanning subqueries (subselects in rangetable).

This is just enough different from sublinks (nodeSubplan.c) to mean that we need two sets of code. Ought to look at trying to unify the cases.

We just return the subplan's result slot, rather than expending extra cycles for ExecCopySlot(). (Our own ScanTupleSlot is used only for EvalPlanQual rechecks.)

SubqueryRecheck -- access method routine to recheck a tuple in EvalPlanQual

Scans the subquery sequentially and returns the next qualifying tuple. We call the ExecScan() routine and pass it the appropriate access method functions.

EXPLAIN identity in core source

case T_SubqueryScan:
			pname = sname = "Subquery Scan";
			break;

EXPLAIN labels in this source build

Text-format labelStructured node identity
Subquery ScanSubquery Scan

Related entries

Documentation and source

Source build
Version
18.6
Build
PostgreSQL 18.6 source archive
Source fingerprint
555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f

Compare versions

PostgreSQL 17 → 18: unchanged.

Compares recorded interfaces and attributes. Source fingerprints and build metadata are excluded; an absent sample is not proof of the introduction or removal release.

Related entries

Export JSON · Back to Plan Nodes · Recorded in PostgreSQL 10 through 20; the first sample is not necessarily its introduction.