Future<List<List<Widget>>> getDetailList(
      List<int> list, String column) async {

    List<Widget> list1 = List();
    List<Widget> list2 = List();
    List<Widget> list3 = List();

    List<List<Widget>> listFromDB = [list1, list2, list3];
    var databasesPath = await getDatabasesPath();
    String path = join(databasesPath, 'books.db');
    Database database = await openDatabase(path, version: 1);
    for (int i = 0; i < list.length; i++) {

      var result = await database.rawQuery(
          'SELECT DISTINCT $column FROM planner WHERE id = ${list[i]}');

          list1.add(_item(result[0][column].toString()));
      }
    }

import 'package:queries/collections.dart';

void main() {
  List<String> list = ["a", "a", "b", "c", "b", "d"];
  var result = new Collection(list).distinct();
  print(result.toList());
}