private String parseConstant(ConstantContext constantContext) {
    String text = constantContext.getText();
    if (constantContext.boolean_literal() != null
        || constantContext.INTEGER_LITERAL() != null
        || constantContext.realLiteral() != null) {
      return text;
    } else if (constantContext.STRING_LITERAL() != null) {
      return parseStringLiteral(text);
    } else if (constantContext.dateExpression() != null) {
      return String.valueOf(
          parseDateExpression(
              constantContext.dateExpression(),
              CommonDescriptor.getInstance().getConfig().getTimestampPrecision()));
    } else {
      throw new IllegalArgumentException("Unsupported constant value: " + text);
    }
  }
function for parsing file path used by LOAD statement.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/parser/ASTVisitor.java