Directions
1. You can use the ROWKEY system column to inspect the key on a KSQL stream or table:
ksql> SELECT ROWKEY, ID, FIRST_NAME, LAST_NAME FROM CUSTOMERS LIMIT 5; 1 | 1 | Bibby | Argabrite 3 | 3 | Marv | Dalrymple 7 | 7 | Marigold | Veld 8 | 8 | Ruperto | Matteotti 5 | 5 | Modestia | Coltart
Here you can see that the key of the message (ROWKEY) being read from the Kafka topic is the same as the ID column.
2. To change the key used for a topic, use the PARTITION BY clause. This can be especially useful for ensuring that topics which are used for KSQL tables are correctly keyed. In this example, you repartition the topic from ID to LAST_NAME:
CREATE STREAM CUSTOMERS_REKEY AS SELECT * FROM CUSTOMERS PARTITION BY LAST_NAME;
3. Use DESCRIBE EXTENDED to confirm that the key has been set:
ksql> DESCRIBE EXTENDED CUSTOMERS_REKEY; Type : STREAM Key field : LAST_NAME [...]
4. Validate on a per-message basis that the key is now as required:
ksql> SELECT ROWKEY, ID, FIRST_NAME, LAST_NAME FROM CUSTOMERS_REKEY LIMIT 5; Yeeles | 4 | Nolana | Yeeles Dalrymple | 3 | Marv | Dalrymple Coltart | 5 | Modestia | Coltart Acaster | 6 | Bram | Acaster Argabrite | 1 | Bibby | Argabrite