Error when using ->* to query struct in pull query

ksqlDB
1

“@type”:“statement_error”,
“error_code”:40001,
“message”:“Cannot cast io.confluent.ksql.parser.tree.StructAll to io.confluent.ksql.parser.tree.SingleColumn”

I got the above error when trying to run a pull query that involves exploding a struct. The same command when run as a push query instead has no issue. I look at the ksqldb docs but it makes no mention that the ->* is valid for push queries only.

2

I’m trying a basic repro below and both push and pull are working. Could you provide your repro? Also try the repro below and make sure it works for you.

Given this setup:

CREATE STREAM s (
    k VARCHAR KEY,
    my_struct STRUCT<
        inner_string VARCHAR,
        inner_int INT
    >
) WITH (
    kafka_topic = 's-topic',
    partitions = 1,
    value_format = 'JSON'
);

INSERT INTO s (
    k, my_struct
) VALUES (
    'the_key', STRUCT(inner_string := 'foo', inner_int := 123)
);

Both of these queries succeed:

SELECT my_struct->* FROM s EMIT CHANGES;

SELECT my_struct->* FROM s WHERE k='the_key';
3

Thank you for the swift reply. I tried your repro and it works for both push and pull query. So it seems it works for Stream. However, when I tried the same but for Table instead of Stream, this is when I got the error.

The steps to reproduce the error is as follows, and I am running Confluent 7.5.2:

CREATE TABLE STRUCT_TEST_TABLE (
  k VARCHAR PRIMARY KEY,
  simple_struct SRUCT<
    inner_string VARCHAR,
    inner_int INT
  >
) with (
  kafka_topic='STRUCT_TEST_TABLE_TOPIC', 
  PARTITIONS=1, 
  VALUE_FORMAT='AVRO'
);

INSERT INTO STRUCT_TEST_TABLE (
    k, simple_struct
) VALUES (
    'the_key', STRUCT(inner_string := 'foo', inner_int := 123)
);

Push queries run with no problem

image
image1496×726 24.5 KB

Pull queries will return the error

image
image1491×698 23.9 KB

This same error also applies when issuing pull queries to explode struct on derived tables.

4

Thank you for the repro - I see the same behavior. I reported this to the ksqlDB team at Confluent.

Are you able to work around by selecting struct fields explicitly, or is the ->* syntax functionally necessary?

5

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