title: Find the employee with max salary in his department
body: <p>Table structure is as below</p>
  
  <pre><code>id  dept    salary
  1   30  2000
  2   20  5500
  3   30  6700
  4   30  8900
  5   30  9900
  6   10  1120
  7   20  8900
  8   10  2400
  9   30  2600
  10  10  2999
  </code></pre>
  
  <p>I need the output to have two columns:</p>
  
  <p>Id and Salary</p>
  
  <p>Id should be unique and salary should have the max salary</p>