CCDAK Apache Kafka Practice Test 2026 – The Complete All-in-One Guide to Exam Success

The thing being tested is how KTable-to-KTable joins determine which records should be combined. In Kafka Streams, these joins pair up records by their keys. That means you typically join on the key that each KTable carries. If the information you want to join on is not currently the key, you can re-key one or both tables by extracting a foreign key from the value and use that as the new join key. In other words, you can perform a join based on the primary key (the existing key) or based on a foreign key you derive by re-keying, which is why the answer reflects “Key Or Foreign-Key Based.” This isn’t a windowed join—the join is defined by matching keys, not a time window.