// TODO: replace this with a table-generating operator that produces 1 row with no columns
QualifiedTableName name = MetadataUtil.createQualifiedTableName(session, QualifiedName.of("dual"));
Optional<TableHandle> optionalHandle = metadata.getTableHandle(name);
checkState(optionalHandle.isPresent(), "Dual table provider not installed");
TableHandle table = optionalHandle.get();
TableMetadata tableMetadata = metadata.getTableMetadata(table);
Map<String, ColumnHandle> columnHandles = metadata.getColumnHandles(table);
checkState(!metadata.getSampleWeightColumnHandle(table).isPresent(), "dual table should not have a sample weight");
ImmutableMap.Builder<Symbol, ColumnHandle> columns = ImmutableMap.builder();