How does Flink SQL read Avro union?

[Vincent Dong]

Hi All, 
  How does Flink SQL read Kafka Avro message which has union field?
  For me,  avro schema is defined as following, 
```
  record ItemRow {
    string num_iid;
    string has_showcase;
    string jdp_created;
  }


  record RefundRow {
    string refund_id;
    string status;
    string jdp_created;
  }


  record RowEvent {
    union { ItemRow, RefundRow } item_row;
  }
```
Now I'm sure that for a specific kafka topic, the item_row in all messages is 
RefundRow, but I don't know how to define source table and query the table. 
Can I define the table to force Flink SQL converts all messages to RefundRow? 
Then I can `select status, refund_id from the_converted_table`.




Thanks
Vincent Dong