title: how to make two 3 columns are unique in SQL server ?
body: <p>I want to make three columns are unique in my data table </p>
  
  <pre><code>-----------------------------------
   Column A  |  Column B | Column C
  ----------------------------------
    Kasun     Cham      Nimith   
  ----------------------------------
    Kasun     Cham      Rox      - This row ok and must be allowed to add.
  ----------------------------------
    Kasun     Cham      Nimith  -  but This row must not be allowed to add again, 
  ---------------------------------
  </code></pre>
  
  <p>how can I accomplish this in SQL server ? </p>