presto-main/src/main/java/io/prestosql/sql/planner/optimizations/UnaliasSymbolReferences.java/Rewriter/visitSample
class Rewriter:        @Override
        public PlanNode visitSample(SampleNode node, RewriteContext<Void> context)
        {
            return new SampleNode(node.getId(), context.rewrite(node.getSource()), node.getSampleRatio(), node.getSampleType());
        }