[Bug][Flink-table-sink] Why add unique key to the pk set when generating sink table schema #181

private String[] getKeyFields(Context context, ReadableConfig config, String databaseName,
      String tableName) {
    // check write mode
    TiDBWriteMode writeMode = TiDBWriteMode.fromString(config.get(WRITE_MODE));
    String[] keyFields = null;
    if (writeMode == TiDBWriteMode.UPSERT) {
      try (ClientSession clientSession = ClientSession.create(
          new ClientConfig(context.getCatalogTable().toProperties()))) {
        Set<String> set = ImmutableSet.<String>builder()
            .addAll(clientSession.getUniqueKeyColumns(databaseName, tableName)) // Why add all unique keys to pk set?
            .addAll(clientSession.getPrimaryKeyColumns(databaseName, tableName))
            .build();
        keyFields = set.size() == 0 ? null : set.toArray(new String[0]);
      } catch (Exception e) {
        throw new IllegalStateException(e);
      }
    }
    return keyFields;
  }