presto-main/src/main/java/io/prestosql/sql/planner/optimizations/UnaliasSymbolReferences.java/UnaliasSymbolReferences/visitMarkDistinct
class UnaliasSymbolReferences:        @Override
        public PlanNode visitMarkDistinct(MarkDistinctNode node, RewriteContext<Void> context)
        {
            PlanNode source = context.rewrite(node.getSource());
            List<Symbol> symbols = canonicalizeAndDistinct(node.getDistinctSymbols());
            return new MarkDistinctNode(node.getId(), source, canonicalize(node.getMarkerSymbol()), symbols, canonicalize(node.getHashSymbol()));
        }