title: Getting unique tuples in SQL
body: <p>i have a table like below i want to get unique values.</p>
  
  <pre><code>from_st     to_st       fare
  ---------------------------
  Bangalore   Hyderabad   600
  Hyderabad   Bangalore   600
  Bangalore   chennai     500
  chennai     Bangalore   500
  Bangalore   noida       1500
  noida       Banagalore  1500
  bangalore   delhi       3000
  bangalore   pune        2000
  </code></pre>
  
  <p>i need data like Bangalore to Hyderabad and Hyderabad to Bangalore are duplicates. so i want only one records among them.</p>
  
  <p>desired output:</p>
  
  <pre><code>from_st     to_st       fare
  ---------------------------
  Bangalore   Hyderabad   600
  Bangalore   chennai     500
  Bangalore   noida       1500
  bangalore   delhi       3000
  bangalore   pune        2000
  </code></pre>