[jira] [Created] (FLINK-20175) Avro Confluent Registry SQL format does not support adding nullable columns

[Shang Yuanchun (Jira)]

Dawid Wysakowicz created FLINK-20175:
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             Summary: Avro Confluent Registry SQL format does not support adding nullable columns
                 Key: FLINK-20175
                 URL: https://issues.apache.org/jira/browse/FLINK-20175
             Project: Flink
          Issue Type: Bug
          Components: Formats (JSON, Avro, Parquet, ORC, SequenceFile)
            Reporter: Dawid Wysakowicz
            Assignee: Dawid Wysakowicz
             Fix For: 1.12.0


The {{AvroSchemaConverter#convertToSchema}} generates a union with "null" for nullable logical types, but it does not set the default value to null. In turn it makes it impossible to generate a backwards compatible schema from a DDL statement.

Example:
1. Create a table: {{CREATE TABLE t (id INT NOT NULL) WITH (/* avro confluent format*/)}}
2. Create a new table over the same topic or alter the old table with {{CREATE TABLE newT(id INT NOT NULL, optionalDescription STRING) WITH (/*avro confluent format*/)}}
3. When reading from {{newT}} records inserted into {{t}} it will fail, because the {{optionalDescription}} has no default value.



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