List<Projection> projections,
int columnIdx,
int projectionIdx,
List<DataType> inputTypes) {
final Projection projection = projections.get(projectionIdx);
final Symbol symbol = projection.outputs().get(columnIdx);
if (symbol instanceof DataTypeSymbol) {
streamers[columnIdx] = ((DataTypeSymbol) symbol).valueType().streamer();
} else if (symbol.symbolType() == SymbolType.AGGREGATION) {
Aggregation aggregation = (Aggregation)symbol;