LINQ查询

子查询

描述：查询订单数超过5的顾客信息

查询句法：

var 子查询 = from c in ctx.Customers                    where                        (from o in ctx.Orders group o by o.CustomerID into o where o.Count() > 5 select o.Key).Contains(c.CustomerID)                    select c;

in 操作

描述：查询指定城市中的客户

查询句法：

var in操作 = from c in ctx.Customers                     where new string[] { "Brandenburg", "Cowes", "Stavern" }.Contains(c.City)                     select c;

Join

描述：内连接，没有分类的产品查询不到

查询句法：

var innerjoin = from p in ctx.Products                         join c in ctx.Categories                         on p.CategoryID equals c.CategoryID                         select p.ProductName;

描述：外连接，没有分类的产品也能查询到

查询句法：

var leftjoin = from p in ctx.Products                        join c in ctx.Categories                        on p.CategoryID equals c.CategoryID                        into pro                        from x in pro.DefaultIfEmpty()                        select p.ProductName;