average method
Calculations
Implementation
@override
Future<double?> average(String column) async {
final builder = _copyQueryWith(columns: ['AVG($column)']);
final completer = Completer<List<Map<String, dynamic>>>()
..complete(database!.rawQuery(builder.sql, builder.arguments));
if (isLogger!) Logger.query(type, completer.future, builder);
final result = await completer.future;
return result.first.values.firstOrNull as double?;
}