Continuous query
A continuous query remains active and incrementally emits updated results as new data arrives.
Kafka Streams in Action, Second Edition
A push query is a continuous ksqlDB query that emits changing results to the client that issued it without persisting those results in a topic.
- How it is used
- Streams ongoing asynchronous query results directly to the requesting client.
- How deep it goes
- Defines execution and delivery behavior, then demonstrates SELECT, WHERE, and LIMIT without detailing query internals.
- Examples
- Uses activity_leaders selections with EMIT CHANGES, a total_steps filter, and a ten-row limit.
- What you can do after
- Apply it via ksqlDB to receive filtered, continually changing stream or table results in a client.
Read how Kafka Streams in Action, Second Edition explains continuous query →
Kafka for Architects
A continuous query is a query that remains active and incrementally updates its results as new data arrives.
- How it is used
- Processes incoming Kafka events continuously to deliver low-latency filtered or aggregated results to downstream consumers.
- How deep it goes
- Explains stream filtering, grouping, and windows, and sketches translation into Kafka Streams applications without low-level implementation details.
- Examples
- Uses expensive-order filtering, per-country counts, and one-hour tumbling-window counts.
- What you can do after
- Build it with ksqlDB by defining a stream, applying SQL transformations, and emitting results to an output topic.
Related concepts
- pull querycontrasts with · A pull query is an on-demand query that retrieves a point-in-time result from current or materialized data and terminates after returning it.
- persistent querycontrasts with · A persistent query is a server-side ksqlDB query whose continuously computed results are stored in a Kafka topic for later consumption.
- SQLuses · SQL is a standardized declarative language for defining, querying, and manipulating data and structures in relational database systems.
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