@Override
  public Optional<Symbol> getAssignedSymbol(
      PlanNode node, SessionInfo sessionInfo, Metadata metadata, SymbolAliases symbolAliases) {
    return symbolAliases.getOptional(alias).map(Symbol::from);
  }
Just check alias is present; return self mapping from symbolAliasesMap.
iotdb-core/datanode/src/test/java/org/apache/iotdb/db/queryengine/plan/relational/planner/assertions/AliasPresent.java