title: How to select rows based on unique column
body: <p>I have table with values as </p>
  
  <pre>
      ColumnA   ColumnB
  
      ASD       A
      CSD       B
      DSD       C
      ESD       D
      FSD       D
      GSD       D
  </pre>
  
  <p>Column A is primary key, I need result as </p>
  
  <pre>
      ColumnA   ColumnB
  
      ASD       A
      CSD       B
      DSD       C
      ESD       D
  </pre>
  
  <p>I want all unique values from column B &amp; their associated first values columnA.</p>
  
  <p>I tried few queries &amp; looked on Google but couldn't find ant solution .</p>
  
  <p>Thanks,
  Rohit.</p>