快速而又肮脏的解决方案是将GroupBy链添加到第一个查询的末尾。

var qry = (from x in CustomersChecks.CustomersChecksList
          where x.RoutingNumber == routingnumber &&
          x.BankAccountNumber == bankAccountNumber &&
          x.Branch > 0 &&
          x.AccountNumber > 0
          orderby x.Name
          select x).GroupBy(x => new { x.Branch, x.AccountNumber})
                   .Select(x => x.First())
                   .ToList();

或者，通过将group by合并到exist查询语法中来执行以下操作

var qry = (from x in CustomersChecks.CustomersChecksList
          where x.RoutingNumber == routingnumber &&
          x.BankAccountNumber == bankAccountNumber &&
          x.Branch > 0 &&
          x.AccountNumber > 0
          orderby x.Name
          group x by new { x.Branch, x.AccountNumber} into grp
          select grp.First()).ToList();

var qry = CustomersChecks.CustomersChecksList.Where(x =>
    x.RoutingNumber == routingnumber &&
    x.BankAccountNumber == bankAccountNumber &&
    x.Branch > 0 &&
    x.AccountNumber > 0).OrderBy(x => x.Name)
    .GroupBy(x => new { x.Branch, x.AccountNumber})
    .Select(x => x.First())
    .ToList();