presto-main/src/main/java/io/prestosql/sql/planner/optimizations/UnaliasSymbolReferences.java/Rewriter/visitExcept
class Rewriter:        @Override
        public PlanNode visitExcept(ExceptNode node, RewriteContext<Void> context)
        {
            return new ExceptNode(node.getId(), rewriteSources(node, context).build(), canonicalizeSetOperationSymbolMap(node.getSymbolMapping()), canonicalizeAndDistinct(node.getOutputSymbols()));
        }