title: group and return rows with the minimum value
body: <p>There is a tasks table.
  <code>id | name | project_id | created | ...</code></p>
  <p>Tasks can be in different projects. I need to return one task from each project with a minimum creation date. Here is my solution</p>
  <pre><code>SELECT *
  FROM tasks a
  JOIN (
      SELECT project_id, min(created) as created
      FROM tasks
      GROUP BY project_id
      ) b
  ON a.project_id=b.project_id AND a.created = b.created;
  </code></pre>
  <p>but if there are points in the project with the same creation dates, then I return two records for one project</p>