LINQ的Group By与Count组合使用

Question

我正在尝试使用LINQ编写查询。

Select UserId, UserNumber 
FROM User
where UserNumber in
(Select UserNumber
        FROM User
        group by UserNumber
        having Count(UserId) = 1)

有什么提示吗？

- gruber

Answer 1

var query = from u in User
            group u by u.UserNumber into usergroup
            where usergroup.Count() == 1
            from item in usergroup
            select new { item.UserId,item.UserNumber };

- Anthony Pegram

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这会生成一个查询吗？还是每个组一个查询？ - Amy B

当User实际上是类似于dbContext.Users时，这是一个单一的查询。 - Sander Rijken

Answer 2

如果你对子查询感兴趣，你可以这样做。

var subquery =
  from u in User
  group u by u.UserNumber into g
  where g.Count() = 1
  select g.Key;

var query =
  from u in User
  where subquery.Any(num => num == u.UserNumber)
  select u;

- Amy B