Into Clause VS Let Clause

1.Into Clause

    用来将select, join,或者group的结果存储到一个临时变量中。

    目的：在之后的查询中需要使用此结果。例如：

 

var developersGroupedByLanguage =    from d in developers    group d by d.Language into developersGrouped    select new {       Language = developersGrouped.Key,       DevelopersCount = developersGrouped.Count()    };foreach (var group in developersGroupedByLanguage) {     Console.WriteLine ("Language {0} contains {1} developers",     group.Language, group.DevelopersCount);}

2.Let Clause

    let子句将一个子表达式的结果存储到一个变量中。

    与SQL语句相比较，let子句产生的变量类似于计算列。即该列是通过对表中若干列进行某种计算获得的。例如对OrderDetail中的UnitPrice * Count得到某商品的总价。

 

var categoriesByProductsNumberQuery =    from c in categories    join p in products on c.IdCategory equals p.IdCategory       into productsByCategory    let ProductsCount = productsByCategory.Count()    orderby ProductsCount    select new { c.IdCategory, ProductsCount};    foreach (var item in categoriesByProductsNumberQuery) {Console.WriteLine(item);}