docs: private String getDistinctColumnName(final String innerExpression) {
          Pattern pattern = Pattern.compile("\\(\\s*DISTINCT\\s+(\\S+)\\s*\\)", Pattern.CASE_INSENSITIVE);
          Matcher matcher = pattern.matcher(innerExpression);
          String result = "";
          if (matcher.find()) {
              result = matcher.group(1);
          }
          return result;
      }