如何在LINQ查询中使用GROUP BY获取MAX行？

Question

我在LINQ中寻找一种方法来匹配后面的SQL查询.

Select max(uid) as uid, Serial_Number from Table Group BY Serial_Number

真的在寻找这方面的一些帮助.由于Group By语法,上面的查询获取每个序列号的最大值.

Answer 1

        using (DataContext dc = new DataContext())
        {
            var q = from t in dc.TableTests
                    group t by t.SerialNumber
                        into g
                        select new
                        {
                            SerialNumber = g.Key,
                            uid = (from t2 in g select t2.uid).Max()
                        };
        }

Answer 2

var q = from s in db.Serials
        group s by s.Serial_Number into g
        select new {Serial_Number = g.Key, MaxUid = g.Max(s => s.uid) }

Answer 3

在方法链形式:

db.Serials.GroupBy(i => i.Serial_Number).Select(g => new
    {
        Serial_Number = g.Key,
        uid = g.Max(row => row.uid)
    });

Answer 4

我已经检查过DamienG在LinqPad中的答案.代替

g.Group.Max(s => s.uid)

应该

g.Max(s => s.uid)

谢谢!

Answer 5

如果您只需要这两个字段,答案就可以了,但对于更复杂的对象,这种方法可能很有用:

from x in db.Serials 
group x by x.Serial_Number into g 
orderby g.Key 
select g.OrderByDescending(z => z.uid)
.FirstOrDefault()

...这将避免"选择新"

Answer 6

这可以使用 LINQ lamda 表达式中的 GroupBy 和 SelectMany 来完成

var groupByMax = list.GroupBy(x=>x.item1).SelectMany(y=>y.Where(z=>z.item2 == y.Max(i=>i.item2)));