Help - Unable to read Key from Kafka messages in Flink SQL Client

[Siva Ram Gujju]

Hello,

I am new to Flink. Running into an issue to read Key from Kafka messages in
Flink SQL Client.

I have an Order Kafka topic with below messages:

Key: {"orderNumber":"1234"}
Value: {"orderDate":"20250528","productId":"Product123"}

I am able to get the key and value by using

kafka-console-consumer.bat --property "print.key=true" --topic Orders
--from-beginning --bootstrap-server xxxxxx


I tried to create a table in Flink SQL:

CREATE TABLE Orders (
      orderNumber STRING,
      orderDate STRING,
      productId STRING
    ) WITH (
      'connector' = 'kafka',
      'topic' = 'Orders',
      'properties.bootstrap.servers' = 'xxxxxx',
      'properties.group.id' = 'FlinkGroupId',
      'format' = 'json',
      'scan.startup.mode' = 'earliest-offset',
      'key.format' = 'json',
      'key.fields' = 'orderNumber;'
    );When I query the table select * from Orders; orderNumber is
printing as "NULL" instead of the actual orderNumber.


   - I tried changing the type to string. Still it is printing as "NULL"
   - If I send a malformed JSON in the key, Flink is throwing an error. So,
   it is clear that Flink is trying to parse the key field as JSON. But why is
   it printing as "NULL" in the select query output?


Can anyone please advise what I am doing wrong?

Thanks,
Siva