Queries Overview

ksqlDB has a rich set of constructs for both storing events in collections and deriving new ones through stream processing. Sometimes, you need to process your events in a real-time stream or by aggregating them together into a materialized table. In these cases, you need a way for your applications or microservices to leverage these collections. That's where queries come in.

Push and pull queries

Queries enable you to ask questions about collections and materialized views. ksqlDB supports two different kinds of client-issued queries: push and pull.

• Pull Queries enable you to look up information at a point in time.
• Push Queries enable you to subscribe to a result as it changes in real-time. You can subscribe to the output of any query, including those that return a stream or a materialized aggregate table.

ksqlDB supports both kinds of queries by using SQL over its REST API. Combining them enables you to build powerful real-time applications.

API Reference

• SELECT (Push Query)
• SELECT (Pull Query)

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Last update: 2020-04-20