title: Remove duplicates if you have only one column with value
body: <p>This is too easy, if you have <code>Id</code> column and <code>Value</code> column which has duplicate rows. But in the interview i had been asked how to remove it, if you have only <code>Value</code> column. For example:</p>
  
  <p>table_a input:</p>
  
  <pre><code>Value
  A
  A
  B
  A
  C
  D
  D
  E
  F
  F
  E
  </code></pre>
  
  <p>table_a output:</p>
  
  <pre><code>Value
  A
  B
  C
  D
  E
  F
  </code></pre>
  
  <p>Question: You have table with only one column <code>Value</code> and you have to <code>delete</code> all rows, which have duplicates (as in result upper).</p>