title: Select distinct in Linq query
body: <p>I've a collection with the data like this.</p>
  
  <pre><code>-------------------------------------------- 
  |  key   | customer Name | code | isActive | 
  --------------------------------------------
  | 30002  |    XYZ        | 234  |     1    |
  --------------------------------------------
  | 30002  |    XYZ        | 234  |     1    |
  --------------------------------------------
  | 30002  |    XYZ        | 234  |     1    |
  --------------------------------------------
  | 30034  |    ERR        | 344  |     1    |
  --------------------------------------------
  | 30031  |    LDD        | 343  |     1    |
  --------------------------------------------
  </code></pre>
  
  <p>how can select the distinct data using linq?</p>