Left Outer Join

Query

public void Linq105() 
{
    string[] categories = new string[]{  
        "Beverages", 
        "Condiments",  
        "Vegetables",  
        "Dairy Products", 
        "Seafood" };
  
    List products = GetProductList();
  
    var q =
        from c in categories
        join p in products on c equals p.Category into ps
        from p in ps.DefaultIfEmpty()
        select new { Category = c, ProductName = p == null ? "(No products)" : p.ProductName };
  
    foreach (var v in q)
    {
        Console.WriteLine(v.ProductName + ": " + v.Category);
    }
}

Lambda Expression

public void Linq105()
{
    List customers = GetCustomerList();
    List suppliers = GetSupplierList();
 
    var supplierCusts =
        suppliers.GroupJoin(customers, sup => sup.Country, cust => cust.Country, (sup, cs) => new {sup, cs})
                    .SelectMany(@t => @t.cs.DefaultIfEmpty(),(@t, c) => new {@t, c})
                    .OrderBy(@t => @t.@t.sup.SupplierName)
                    .Select(@t => new{
                        Country = @t.@t.sup.Country,
                        CompanyName = @t.c == null? "(No customers)": @t.c.CompanyName,
                        SupplierName = @t.@t.sup.SupplierName});
 
    foreach (var item in supplierCusts)
    {
        Console.WriteLine("{0} ({1}): {2}", item.SupplierName, item.Country, item.CompanyName);
    }
}

Output

Chai: Beverages
Chang: Beverages
GuaranÃ¡ FantÃ¡stica: Beverages
Sasquatch Ale: Beverages
Steeleye Stout: Beverages
CÃ´te de Blaye: Beverages
Chartreuse verte: Beverages
Ipoh Coffee: Beverages
Laughing Lumberjack Lager: Beverages
Outback Lager: Beverages
RhÃ¶nbrÃ¤u Klosterbier: Beverages
LakkalikÃ¶Ã¶ri: Beverages
Aniseed Syrup: Condiments
Chef Anton's Cajun Seasoning: Condiments
Chef Anton's Gumbo Mix: Condiments
Grandma's Boysenberry Spread: Condiments
Northwoods Cranberry Sauce: Condiments
Genen Shouyu: Condiments
Gula Malacca: Condiments
Sirop d'Ã©rable: Condiments
Vegie-spread: Condiments
Louisiana Fiery Hot Pepper Sauce: Condiments
Louisiana Hot Spiced Okra: Condiments
Original Frankfurter grÃ¼ne SoÃŸe: Condiments
(No products): Vegetables
Queso Cabrales: Dairy Products
Queso Manchego La Pastora: Dairy Products
Gorgonzola Telino: Dairy Products
Mascarpone Fabioli: Dairy Products
Geitost: Dairy Products
Raclette Courdavault: Dairy Products
Camembert Pierrot: Dairy Products
Gudbrandsdalsost: Dairy Products
Flotemysost: Dairy Products
Mozzarella di Giovanni: Dairy Products
Ikura: Seafood
Konbu: Seafood
Carnarvon Tigers: Seafood
Nord-Ost Matjeshering: Seafood
Inlagd Sill: Seafood
Gravad lax: Seafood
Boston Crab Meat: Seafood
Jack's New England Clam Chowder: Seafood
Rogede sild: Seafood
Spegesild: Seafood
Escargots de Bourgogne: Seafood
RÃ¶d Kaviar: Seafood