private boolean containsCorrelation(PlanNode node, List<Symbol> correlation) {
    return Sets.union(
            SymbolsExtractor.extractUnique(node, lookup),
            SymbolsExtractor.extractOutputSymbols(node, lookup))
        .stream()
        .anyMatch(correlation::contains);
  }
@return constant symbols from a perspective of a subquery
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/planner/optimizations/PlanNodeDecorrelator.java