正如@cricket\u007引用的那样，在ksql中有一个以这种方式处理空值的开放票证。
您可以使用的一种解决方法是使用insert-into。它不是很优雅，当然也不像 COALESCE :

# Set up some sample data, run this from bash

# For more info about kafkacat see

# https://docs.confluent.io/current/app-development/kafkacat-usage.html

    kafkacat -b kafka-broker:9092 \
            -t topic_with_nulls \
            -P <<EOF
{"col1":1,"col2":16000,"col3":"foo"}
{"col1":2,"col2":42000}
{"col1":3,"col2":94000,"col3":"bar"}
{"col1":4,"col2":12345}
EOF

下面是处理 col3 :

-- Register the topic
CREATE STREAM topic_with_nulls (COL1 INT, COL2 INT, COL3 VARCHAR) \
  WITH (KAFKA_TOPIC='topic_with_nulls',VALUE_FORMAT='JSON');

-- Query the topic to show there are some null values
ksql> SET 'auto.offset.reset'='earliest';
Successfully changed local property 'auto.offset.reset' from 'null' to 'earliest'
ksql> SELECT COL1, COL2, COL3 FROM topic_with_nulls;
1 | 16000 | foo
2 | 42000 | null
3 | 94000 | bar
4 | 12345 | null

-- Create a derived stream, with just records with no NULLs in COL3
CREATE STREAM NULL_WORKAROUND AS \
  SELECT COL1, COL2, COL3 FROM topic_with_nulls WHERE COL3 IS NOT NULL;

-- Insert into the derived stream any records where COL3 *is* NULL, replacing it with a fixed string
INSERT INTO NULL_WORKAROUND \
  SELECT COL1, COL2, 'N/A' AS COL3 FROM topic_with_nulls WHERE COL3 IS NULL;

-- Confirm that the NULL substitution worked
ksql> SELECT COL1, COL2, COL3 FROM NULL_WORKAROUND;
1 | 16000 | foo
2 | 42000 | N/A
3 | 94000 | bar
4 | 12345 | N/A