private Expression parseScalarFunctionExpression(
      IoTDBSqlParser.ScalarFunctionExpressionContext context, boolean canUseFullPath) {
    if (context.CAST() != null) {
      return parseCastFunction(context, canUseFullPath);
    } else if (context.REPLACE() != null) {
      return parseReplaceFunction(context, canUseFullPath);
    } else if (context.ROUND() != null) {
      return parseRoundFunction(context, canUseFullPath);
    } else if (context.SUBSTRING() != null) {
      return parseSubStrFunction(context, canUseFullPath);
    }
    throw new UnsupportedOperationException();
  }
function for parsing file path used by LOAD statement.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/parser/ASTVisitor.java