Question

我在LINQ中寻找一种匹配后续SQL查询的方法。

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

以方法链形式：

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

Answer 4

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“选择新的”

Answer 5

这可以在LINQ lamda表达式中使用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)));

如何在LINQ查询中使用GROUP BY获取MAX行？

6 个答案: