Fix query grouping clause in DistinctLengths query

Author: dandanlen

src/explorer/Queries/DistinctLengths.cs

@@ -19,7 +19,7 @@ protected override string GetQueryStatement(string table, string column)
                     count(*),
                     count_noise(*)
                 from {table}
-                group by {column}";
+                group by 1";
         }
     }
 }