title: Selecting rows with unique field values in mysql
body: <p>I have these columns for table <code>comments</code>:</p>
  
  <pre><code>id
  content
  add_date
  uid
  school_id
  </code></pre>
  
  <p>Rows can have the same school_id.</p>
  
  <p>I want to select the latest data according to add_date, but only <strong>1 row per school_id</strong> (no duplicate for <code>school_id</code>) with  limit of 10.</p>
  
  <p>I've tried many codes already and its not working for me.
  Any help would be appreciated.</p>