presto-main/src/main/java/io/prestosql/sql/planner/QueryPlanner.java/QueryPlanner/outputExpressions
class QueryPlanner:    private List<Expression> outputExpressions(List<SelectExpression> selectExpressions)
    {
        ImmutableList.Builder<Expression> result = ImmutableList.builder();
        for (SelectExpression selectExpression : selectExpressions) {
            if (selectExpression.getUnfoldedExpressions().isPresent()) {
                result.addAll(selectExpression.getUnfoldedExpressions().get());
            }
            else {
                result.add(selectExpression.getExpression());
            }
        }
        return result.build();
    }