Flink SQL AVG with mandatory type casting

[Georg Heiler]

Hi,

I observe strange behavior in Flink SQL:
For an input stream:

CREATE TABLE input_stream (
    duration int,
    rating int

) WITH (
    'connector' = 'kafka',
    'topic' = 't',
    'scan.startup.mode' = 'earliest-offset',
    'format' = 'avro-confluent',
    'avro-confluent.schema-registry.url' = 'http://localhost:8081/',
    'properties.group.id' = 'flink-test-001',
    'properties.bootstrap.servers' = 'localhost:9092'
);

The following SQL:
SELECT AVG(duration) AS  duration_mean, AVG(CAST(rating AS DOUBLE)) AS
rating_mean FROM input_stream;

returns:

duration_mean                    rating_mean
            45              2.503373819163293

I.e. duration_mean is truncated to an INT!

Any other database system I know by default outputs a DOUBLE type for any
input (including INT) and does not truncate it.

Why does Flink decide to truncate here? Why is a manual type cast necessary?

Best,
Georg