@Override
    protected Boolean visitIfExpression(IfExpression node, Void context) {
      ImmutableList.Builder<Expression> expressions =
          ImmutableList.<Expression>builder().add(node.getCondition()).add(node.getTrueValue());

      if (node.getFalseValue().isPresent()) {
        expressions.add(node.getFalseValue().get());
      }

      return expressions.build().stream().allMatch(expression -> process(expression, context));
    }
visitor returns true if all expressions are constant with respect to the group.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/analyzer/AggregationAnalyzer.java