Keys Unlocked - ksqlDB 0.15 Supports Even More Data Types

What this post added

This post introduces significant enhancements to ksqlDB 0.15, primarily focusing on message key capabilities. Key contributions include: 1. Support for all serialization formats (JSON, AVRO, PROTOBUF, DELIMITED, KAFKA, JSON_SR) for message keys. 2. Expanded data type support for keys, including ARRAY, STRUCT, and nested combinations, with specific considerations for MAP types and single-field wrapping. 3. Introduction of composite keys, allowing multiple columns to form a single key. 4. Enhanced PARTITION BY and GROUP BY clauses to accept multiple expressions, leading to tables and streams with multiple key or primary key columns respectively. This directly impacts how data is structured, partitioned, and aggregated within ksqlDB.