`asof_join`

Generic Description

Joins each left event to the latest right event at or before its timestamp. It is documented separately because time construction, sequence ordering, window parameters, and as-of behavior materially change analytical meaning.

Simple example:

WITH [{ts: 1735689600000, value: 10.0, state: 'ok'}, {ts: 1735689660000, value: 13.0, state: 'ok'}, {ts: 1735689840000, value: 9.0, state: 'warn'}, {ts: 1735690200000, value: 16.0, state: 'ok'}] AS readings, [{ts: 1735689300000, state: 'baseline'}, {ts: 1735689720000, state: 'release'}] AS context
RETURN asof_join(readings, context, 900000) AS joined_rows

Consumer-Level Explanation

Use it when context should be historical as-of state, never future state. Prefer this function when the temporal assumption should be visible to the planner, especially for event streams, freshness checks, and sequence features.

More Detailed Explanation

asof_join works on ordered temporal or sequence-style values inside Cypher. The practical contract is to assemble the sequence deliberately, choose the time or window parameter explicitly, and return named fields so downstream planner tooling does not invent unsupported window syntax.

Advanced Example

This example names the event stream and operational context before applying asof_join, which helps planner tooling preserve the intended sequence semantics.

WITH 'sensor-1' AS subject_id,
     [{ts: 1735689600000, value: 10.0, state: 'ok'}, {ts: 1735689660000, value: 13.0, state: 'ok'}, {ts: 1735689840000, value: 9.0, state: 'warn'}, {ts: 1735690200000, value: 16.0, state: 'ok'}] AS readings,
     [{ts: 1735689300000, state: 'baseline'}, {ts: 1735689720000, state: 'release'}] AS context
RETURN subject_id,
       asof_join(readings, context, 900000) AS joined_rows

Real Use Cases

Real Limitations And Tradeoffs