code: private String getTargetColumnName(String sourceColumnName, String alias) {
      String targetColumnName = alias;
      Schema obj = this.getMetadataColumnMap().get(sourceColumnName.toLowerCase());
      if (obj == null) {
        targetColumnName = (targetColumnName == null ? "unknown" + this.unknownColumnCounter : targetColumnName);
        this.unknownColumnCounter++;
      } else {
        targetColumnName = (StringUtils.isNotBlank(targetColumnName) ? targetColumnName : sourceColumnName);
      }
      targetColumnName = this.toCase(targetColumnName);
      return Utils.escapeSpecialCharacters(targetColumnName, ConfigurationKeys.ESCAPE_CHARS_IN_COLUMN_NAME, "_");
    }
docs: Get target column name if column is not found in metadata, then name it
  as unknown column If alias is not found, target column is nothing but
  source column
  
  @param sourceColumnName
  @param alias
  @return targetColumnName