public static boolean containsDiffFunction(Expression expression) {
    if (expression instanceof FunctionCall
        && "diff".equalsIgnoreCase(((FunctionCall) expression).getName().toString())) {
      return true;
    }

    if (!expression.getChildren().isEmpty()) {
      for (Node node : expression.getChildren()) {
        if (containsDiffFunction((Expression) node)) {
          return true;
        }
      }
    }

    return false;
  }
Evaluates an expression's response to binding the specified input symbols to NULL
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/planner/optimizations/PushPredicateIntoTableScan.java