[LINQ] sql 에는 없는 키워드 - let

To introduce an identifier by using let

• You can use the let keyword to introduce an identifier for any expression result in the query expression. This identifier can be a convenience, as in the following example, or it can enhance performance by storing the results of an expression so that it does not have to be calculated multiple times.

  C#

  // studentQuery5 is an IEnumerable<string> 
  // This query returns those students whose 
  // first test score was higher than their 
  // average score. 
  var studentQuery5 =
      from student in students
      let totalScore = student.Scores[0] + student.Scores[1] +
          student.Scores[2] + student.Scores[3]
      where totalScore / 4 < student.Scores[0]
      select student.Last + " " + student.First;
  
  foreach (string s in studentQuery5)
  {
      Console.WriteLine(s);
  }
  
  // Output: 
  // Omelchenko Svetlana 
  // O'Donnell Claire 
  // Mortensen Sven 
  // Garcia Cesar 
  // Fakhouri Fadi 
  // Feng Hanying 
  // Garcia Hugo 
  // Adams Terry 
  // Zabokritski Eugene 
  // Tucker Michael
  

  For more information, see let clause (C# Reference).