debug #888, fix can't calculate max(bytes_on_disk)

pkg/clickhouse/clickhouse.go

@@ -1157,6 +1157,7 @@ func (ch *ClickHouse) CalculateMaxFileSize(ctx context.Context, cfg *config.Conf
 	if !cfg.General.UploadByPart {
 		maxSizeQuery = "SELECT toInt64(max(data_by_disk) * 1.02) AS max_file_size FROM (SELECT disk_name, max(toInt64(bytes_on_disk)) data_by_disk FROM system.parts GROUP BY disk_name)"
 	}
+	maxSizeQuery += " SETTINGS empty_result_for_aggregation_by_empty_set=0"
 	if err := ch.SelectSingleRow(ctx, &rows, maxSizeQuery); err != nil {
 		return 0, fmt.Errorf("can't calculate max(bytes_on_disk): %v", err)
 	}