title: How can I retrieve not except NULL with GROUP_CONCAT in query builder in symfony?
body: <p>In symfony, I join table user(id, email) and table useCases(id, userId, caseType) (relations is OneToMany) like this:</p>
  <pre><code>public function getQueryBuilder()
      {
          $qb = $this-&gt;userRepository-&gt;createQueryBuilder('u');
          $qb-&gt;select(
              '
                  u.id,
                  u.email,
                  GROUP_CONCAT(DISTINCT(CONCAT(IFNULL(uc.caseType,&quot;NULL&quot;)))) as dfCaseType,
                  
              '
          )
              -&gt;leftJoin('u.userCases', 'uc')
              -&gt;orderBy(&quot;u.id&quot;, &quot;DESC&quot;);
  
          return $qb;
      }
  
  public function getById($id)
      {
          $qb = $this-&gt;getQueryBuilder()
              -&gt;where('u.id = :id')
              -&gt;setParameter('id', $id);
          $result = $qb-&gt;groupBy('u.id')-&gt;setMaxResults(1)-&gt;getQuery()-&gt;getOneOrNullResult();
          return $result;
      }
  
  </code></pre>
  <p>I test query on Sequel Pro, and it's OK, here is query:</p>
  <pre><code>select user.id, user.email, GROUP_CONCAT(DISTINCT(CONCAT(IFNULL(`caseType`,'NULL')))) as dfCaseType from user, userCases where  user.id = userCases.userId AND user.id = 44613
  </code></pre>
  <p>and here is result:</p>
  <pre><code>id   emai               dfCaseType
  1   aaa@gmail.com.       0,1,2,3,NULL
  </code></pre>
  <p>But when I apply in project symfony with query builder , it error :</p>
  <pre><code>[Syntax Error] line 0, col 231: Error: Expected Doctrine\ORM\Query\Lexer::T_IDENTIFIER, got '('
  </code></pre>
  <p>Please help me,  thanks!</p>