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Creating a KTable table in Flink requires declaring the primary key on the table. The primary key definition also controls which fields should end up in Kafka’s key. Therefore, we don’t need the ‘key.fields’ option in KTable connector. By default, primary key fields will also be stored in Kafka’s value as well. But users can still use option ‘value.fields-include’ to control this behavior.

KTable Source

Generally speaking, the underlying topic of KTable source MUST be compacted. But users can still be able to create a KTable source on a non-compacted topic. Besides, the underlying topic must have all the data with the same key in the same partition, otherwise, the result will be wrong.

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