title: Update one dataset with another without using PROC SQL
body: <p>I have the below two datasets</p>
  
  <p>Dataset A</p>
  
  <pre><code>id age  mark
  1  .    .
  2  .    .
  1  .    .
  </code></pre>
  
  <p>Dataset B</p>
  
  <pre><code>id age mark
  2  20  200
  1  10  100
  </code></pre>
  
  <p>I need the below dataset as output</p>
  
  <p>Output Dataset</p>
  
  <pre><code>id age mark
  1  10  100
  2  20  200
  1  10  100
  </code></pre>
  
  <p>How to carry out this without using <strong>PROC SQL</strong> i.e. using <strong>DATA STEP</strong>?</p>