LINQ to SQL实体/记录重复？

var query = from item in db.Items
            select item.Name;
var distinctItems = query.Distinct();

var query = from item in db.Items
            group item by item.Name into g
            select new { Name = g.Key, Count = g.Count() };

var query = from item in db.Items
            join category in db.Categories on item.CategoryID equals category.ID
            select new { item.Name, category.Name };