CREATE STREAM ORDERS ( ... ) WITH (
  KAFKA_TOPIC='orders.prod',
  VALUE_FORMAT='json'
);

SELECT * FROM ORDERS WHERE ROWKEY = 'order-123'

1553124285000 | order-123 | ... | ... | ...

CREATE STREAM ORDERS_REKEYED WITH (PARTITIONS=6, REPLICAS=2)
  AS SELECT * FROM ORDERS PARTITION BY LEGACY_ID;

SELECT * FROM ORDERS_REKEYED WHERE ROWKEY = 'abc'

1553124285000 | abc | order-123 | ... | ... | ...
1553124285000 | abc | order-123 | ... | ... | ...
1553124285000 | abc | order-123 | ... | ... | ...
1553124285000 | abc | order-123 | ... | ... | ...