`samplemerge`

Generic Description

samplemerge merges partial aggregate states for returns a representative sampled value. It should receive state produced by the matching state function rather than ordinary business values.

Simple example:

MATCH (d:Document)
WITH samplestate(properties(d).prize) AS partial
RETURN samplemerge(partial) AS value

Consumer-Level Explanation

Use samplemerge when the graph pattern has already selected the row grain and the next step is a trustworthy metric, not another traversal. Keep the aggregate in Cypher when planner visibility, grouped execution, materialized aggregate views, or assistant-authored query validation matter.

More Detailed Explanation

samplemerge operates after MATCH, WHERE, WITH, procedure output, or document/map projection has shaped rows. For planner tooling the important distinction is whether this page documents a final aggregate, a state producer, or a state merger. Final aggregates return business-facing values; state functions return execution-facing summaries; merge functions combine those summaries and should not be treated as ordinary scalar math.

Advanced Example

This example puts samplemerge after graph matching and time bucketing so the aggregate summarizes an explicit business grain rather than an accidental stream of rows.

MATCH (u:User)-[e:VIEWED]->(d:Document)
TIME e.ts BETWEEN datetime('2025-01-01T00:00:00Z') AND datetime('2025-02-01T00:00:00Z')
WITH date_trunc('day', e.ts) AS day_bucket,
     samplestate(properties(d).prize) AS partial_state
RETURN day_bucket,
       samplemerge(partial_state) AS merged_metric
ORDER BY day_bucket

Real Use Cases

Real Limitations And Tradeoffs