Linq 基本語法-Select

在看Apress.Pro LINQ(作者Joseph C. Rattz,Jr.)這本書時
看到這段範例(稍微改寫過)
Example1
首先定義一個字串陣列presidents

string[] presidents = {"Adams", "Arthur", "Buchanan", "Bush", "Carter", "Cleveland",    

"Clinton", "Coolidge", "Eisenhower", "Fillmore", "Ford", "Garfield",    

"Grant", "Harding", "Harrison", "Hayes", "Hoover", "Jackson",    

"Jefferson", "Johnson", "Kennedy", "Lincoln", "Madison", "McKinley",    

"Monroe", "Nixon", "Pierce", "Polk", "Reagan", "Roosevelt", "Taft",    

"Taylor", "Truman", "Tyler", "Van Buren", "Washington", "Wilson"};

Select語法:

var nameObjs = presidents.Select((p,i) => new { Index=i, Name=p });

StringBuilder sb = new StringBuilder();

foreach (var item in nameObjs)

{

  string name = string.Format(@"{0}. {1}",item.Index+1,item.Name);

  sb.AppendLine(name);

}

richTextBox1.Text = sb.ToString();

最後產生的結果如下

Example2(SelectMany用法)

Employee[] employees = Employee.GetEmployeesArray();

EmployeeOptionEntry[] empOptions = EmployeeOptionEntry.GetEmployeeOptionEntries();

var employeeOptions = employees

.SelectMany(e => empOptions

.Where(eo => eo.id == e.id)

.Select(eo => new {

id = eo.id,

optionsCount = eo.optionsCount }));

foreach (var item in employeeOptions)

  Console.WriteLine(item);

其實看完這個範例，我還是依舊不懂
所以上網查了一下，看到這兩篇文章
http://www.tzwhx.com/newOperate/html/1/11/112/14415.html
http://www.cnblogs.com/aspnet2008/archive/2008/12/19/1357690.html
大概看了一下，好像是因為Linq語法並沒有SQL的Join
才會有SelectMany這個方法，我不確定先記錄下來!