.net 如何在 LINQ 查询中使用 GROUP BY 获取 MAX 行？
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How do I get the MAX row with a GROUP BY in LINQ query?
提问by SpoiledTechie.com
I am looking for a way in LINQ to match the follow SQL Query.
我正在 LINQ 中寻找一种方法来匹配以下 SQL 查询。
Select max(uid) as uid, Serial_Number from Table Group BY Serial_Number
Really looking for some help on this one. The above query gets the max uid of each Serial Number because of the Group BySyntax.
真的在寻找一些帮助。由于Group By语法的原因，上述查询获取每个序列号的最大 uid 。
采纳答案by tvanfosson
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()
};
}
回答by DamienG
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) }
回答by Lu55
In methods chain form:
在方法链形式中：
db.Serials.GroupBy(i => i.Serial_Number).Select(g => new
{
Serial_Number = g.Key,
uid = g.Max(row => row.uid)
});
回答by denis_n
I've checked DamienG's answer in LinqPad. Instead of
我在 LinqPad 中检查了 DamienG 的回答。代替
g.Group.Max(s => s.uid)
should be
应该
g.Max(s => s.uid)
Thank you!
谢谢！
回答by Javier
The answers are OK if you only require those two fields, but for a more complex object, maybe this approach could be useful:
如果您只需要这两个字段，答案是可以的，但是对于更复杂的对象，这种方法可能有用：
from x in db.Serials
group x by x.Serial_Number into g
orderby g.Key
select g.OrderByDescending(z => z.uid)
.FirstOrDefault()
... this will avoid the "select new"
...这将避免“选择新的”
