Kafka CASE error fieldSchema for field cannot be null - apache-kafka

Question

I cannot run CASE expression on KSQL.
I set up a stream called api_log. The api_log stream consists of these information.
ksql> describe extended api_log;
Name : API_LOG
Type : STREAM
Key field :
Key format : STRING
Timestamp field : CREATED_ON
Value format : AVRO
Kafka topic : api.api_log(partitions: 1, replication: 1)
Field | Type
----------------------------------------------
ROWTIME | BIGINT (system)
ROWKEY | VARCHAR(STRING) (system)
ID | BIGINT
CREATED_ON | BIGINT
UPDATED_ON | BIGINT
API_CODE | VARCHAR(STRING)
API_MESSAGE | VARCHAR(STRING)
API_KEY | VARCHAR(STRING)
----------------------------------------------
Local runtime statistics
------------------------
(Statistics of the local KSQL server interaction with the Kafka topic api.api_log)
I try to use CASE for my KSQL syntax.
select api_log.status,
case
when api_log.status = 200 then 'success'
else 'error' end as status
from api_log limit 3;
It shows this result.
fieldSchema for field status cannot be null.
However, when I try to execute
ksql> select status from api_log limit 10;
200
200
200
200
200
200
200
200
200
200
Limit Reached
Query terminated
They are not null values.
Why it is not working????

Answer 1

What version of KSQL are you using?
I've just tried to recreate this in my environment running KSQL 5.3.0, and got an expected error (and better error message!):
ksql> select api_log.status,
>case
> when api_log.status = 200 then 'success'
> else 'error' end as status
>from api_log limit 3;
Cannot create field because of field name duplication STATUS
Statement: select api_log.status,
case
when api_log.status = 200 then 'success'
else 'error' end as status
from api_log limit 3;
Caused by: Cannot create field because of field name duplication STATUS
To solve this you should provide a different alias for the second status field:
ksql> select api_log.status,
>case
> when api_log.status = 200 then 'success'
> else 'error' end as human_status
>from api_log limit 3;
407 | error
404 | error
302 | error
Limit Reached
Query terminated