private Expression parseCastFunction(
      IoTDBSqlParser.ScalarFunctionExpressionContext castClause, boolean canUseFullPath) {
    FunctionExpression functionExpression = new FunctionExpression(CAST_FUNCTION);
    functionExpression.addExpression(parseExpression(castClause.castInput, canUseFullPath));
    functionExpression.addAttribute(CAST_TYPE, parseAttributeValue(castClause.attributeValue()));
    return functionExpression;
  }
function for parsing file path used by LOAD statement.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/parser/ASTVisitor.java