LINQ to SQL是否有“with ties”选项？

Question

我正在尝试将以下查询移植到Linq-to-sql，这是否可能？

select * from (
Select top (@Percent) percent with ties *
from(
    Select distinct
      LoanNumber as LoanNo
    From CHE 
    Left Join RecordingInfo as Rec
    On CHE.LoanNumber = Rec.LoanNo
    Where Channel = 'LINX'
        and CHE.Doc in ('MTG','MOD')
        and Rec.LoanNo is null
        and LoanNumber >= '@LoanNo'
) A
order by LoanNo @Order
) B
order by LoanNo

我还没有看到在linq中处理关联的方法。

- Maslow

Answer 1

我认为这样的东西适合你。

public static IQueryable<T> TopPercentWithTies<T, TKey>(this IOrderedQueryable<T> query, Expression<Func<T, TKey>> groupByExpression, double percent)
{
    var groupedQuery = query.GroupBy(groupByExpression);
    int numberToTake = groupedQuery.Count() * percent / 100;
    return groupedQuery.Take(numberToTake).SelectMany(t => t);
}

我只测试了IEnumerable，所以不确定它是否可以正确地与IQueryable一起使用。在调用TopPercentWithTies（）之前，我还对列表进行了排序。

这是我用来测试的代码。

int percent = 50;
var people = new []
{
    new { Age = 99, Name = "Adam" },
    new { Age = 99, Name = "Andrew" },
    new { Age = 89, Name = "Bob" },
    new { Age = 50, Name = "Cecil" },
    new { Age = 50, Name = "Doug" },
    new { Age = 50, Name = "Everett" },
    new { Age = 35, Name = "Frank" },
    new { Age = 25, Name = "Greg" },
    new { Age = 15, Name = "Hank" }
};
var sortedPeople = people.AsQueryable().OrderByDescending(person => person.Age);
var results = sortedPeople.TopPercentWithTies(person => person.Age, percent);
foreach (var person in results)
    Console.WriteLine(person);

希望这能对您有所帮助，或者至少指明了正确的方向。您可能需要调整计算numberToTake的逻辑。

- Ecyrb

---

非常不错。虽然我期望它会是IOrderedQueryable的扩展。 - Maslow

哦，太好了。我不知道有IOrderedQueryable这个东西。我已经更新了代码。 - Ecyrb

这看起来不像会产生类似于 T-SQL TOP n PERCENT WITH TIES 的结果。考虑数据 1 2 2 3 3 3 4 4 4 4 ... 100，它有5050个条目。TOP 1 PERCENT WITH TIES 将返回55行（最高值为 10），而您的函数仅返回1行。 - Ben Voigt

没有点踩，但是这个答案不像 WITH TIES 那样工作。正如 Ben Voigt 所述，如果你考虑数据集 {3 2 2 1 1 0}，结果集将会是 {3 2 2 1 1}，而它（与绑定行为一样）应该是 {3 2 2}。 - Saro Taşciyan