var db = new BigDataEntities();
        var g =
            db.Tab1
                .GroupJoin(db.Tab1, a => a.id, b => b.id, (a, b) => new {a, b})
                .GroupJoin(db.Tab1, c => c.a.id, d => d.id, (c, d) => new {c, d})
                .Select(t => t.c.b.id);    //这里如果用 t.c.a.id就没有错误，用b.id就找不到id了，什么原因，怎么解决呢。但是用join是可以的。

Group Join
 
(back to top)
 
Using a group join you can get all the products that match a given category bundled as a sequence.
 
 
 
复制代码 

C#
 

public void Linq103() 
{ 
    string[] categories = new string[]{  
        "Beverages",  
        "Condiments",  
        "Vegetables",  
        "Dairy Products",  
        "Seafood" }; 
  
    List<Product> products = GetProductList(); 
  
    var q = 
        from c in categories 
        join p in products on c equals p.Category into ps 
        select new { Category = c, Products = ps }; 
  
    foreach (var v in q) 
    { 
        Console.WriteLine(v.Category + ":"); 
        foreach (var p in v.Products) 
        { 
            Console.WriteLine("   " + p.ProductName); 
        } 
    } 
}