使用列的默认值创建 KSQL stream？

Question

Is it possible to create a stream from Kafka topic with default values or fixed value for a few columns which are not present in the topic?

create stream test
(
Balance BIGINT,
Name STRING <---- want to specify a fix value ("NA" or "no name")  for this column which is not in topic data
)
with (kafka_topic='test_topic', value_format='JSON');

Answer 1

You can't do this on the creation of the initial stream against the topic, but you could create a derived stream using coalesce :

create stream test
    (Balance BIGINT,
     Name    STRING )
    with (kafka_topic='test_topic', value_format='JSON');

create stream test_2 AS
    SELECT BALANCE, 
           COALESCE(Name, 'No Name') as name
    from test;