title: SQL select rows only once
body: <p>I have table <code>pro</code> like this :</p>
  
  <pre><code>id    category   details
  1         f        weqweq
  2         m        dqweq
  3         f        xcxzc
  4         m        eqweqw
  5         f        asweq
  6         c        xzsda
  </code></pre>
  
  <p>Now if i try something like :</p>
  
  <pre><code>SELECT DISTINCT category FROM pro
  </code></pre>
  
  <p>i get only <code>m</code> and <code>c</code> </p>
  
  <p>if i try :</p>
  
  <pre><code>  SELECT category FROM pro GROUP BY category
  </code></pre>
  
  <p>i get only <code>f</code> and <code>c</code></p>
  
  <p>How i can query to get all <code>m,f,c</code> only once?!</p>