@Override
                public Object read(SourceRecord record) {
                    final Envelope.Operation op = Envelope.operationFor(record);
                    if (op != Envelope.Operation.UPDATE) {
                        return null;
                    }
                    return record;
                }
The update-before data for UPDATE record.
inlong-sort/sort-flink/sort-flink-v1.13/sort-connectors/mysql-cdc/src/main/java/org/apache/inlong/sort/cdc/mysql/table/MySqlReadableMetadata.java