title: Select parents which don't have a child with specific value
body: <p>Let's image we have two tables:
  PARENT (<code>id</code> INT) and CHILD (<code>parent_id</code> INT, <code>priority</code> INT)</p>
  <p>We have 3 parents and its childs:</p>
  <blockquote>
  <p>Parent_1 (id: 1) with Child_1 (priority: 1)</p>
  <p>Parent_2 (id: 2) with Child_2 (priority: null)</p>
  <p>Parent_3 (id: 3) with Child_3 (priority: 1) and Child_4 (priority: null)</p>
  </blockquote>
  <p>I've tried to use this SQL:</p>
  <pre><code>SELECT `parents`.* FROM `parents` LEFT OUTER JOIN `childs` ON `childs`.`parent_id` = `parent`.`id` WHERE `parents`.`id` IN (1, 2, 3) AND (childs.priority != 1 OR childs.priority IS NULL)
  </code></pre>
  <p>So I expect the result to select Parent_2 only because a check for <code>childs.priority != 1</code> applies here and check <code>childs.priority IS NULL</code> applies here also, but it outputs also Parent_3 because Child_4 passes check <code>childs.priority IS NULL</code>, but it shouldn't show up, because Child_3 doesn't pass <code>childs.priority != 1</code> this check</p>