// returned context.
outContext = new PlanContext(planContext);
SymbolTable inTable = planContext.getSymbolTable();
SymbolTable outTable = new HashSymbolTable(inTable);
outputFields = distinctFields(outputFields);
outTable.addAll(mFieldSymbols);
Schema outputSchema = createFieldSchema(outputFields);
ProjectionNode cleanupProjection = new ProjectionNode(outputFields, outputFields);
cleanupProjection.setAttr(PlanNode.OUTPUT_SCHEMA_ATTR, outputSchema);
flowSpec.attachToLastLayer(cleanupProjection);