php - Query from repository gives back semantical error - not sure why

I'm rather new to Symfony, and I am playing a bit with it. I'm following the SymfonyCast tutorial and just updating my project, learning as I go.

So I have aQuestion entity, andAnswer entity. One question can have many answers, and so my entities look like this:

Answer:

<?php

namespace App\Entity;

use App\Repository\AnswerRepository;
use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Entity(repositoryClass=AnswerRepository::class)
 */
class Answer
{
  /**
   * @ORM\Id()
   * @ORM\GeneratedValue()
   * @ORM\Column(type="integer")
   */
  private $id;

  /**
   * @ORM\Column(type="string", length=255)
   */
  private $content;

  /**
   * @ORM\Column(type="bigint", nullable=true)
   */
  private $vote = 0;

  /**
   * @ORM\ManyToOne(targetEntity="Question")
   */
  private $question;

  /**
   * @ORM\ManyToOne(targetEntity=User::class, inversedBy="answers")
   * @ORM\JoinColumn(nullable=false)
   */
  private $author;

  public function getId(): ?int
  {
    return $this->id;
  }

  public function getContent(): ?string
  {
    return $this->content;
  }

  public function setContent(string $content): self
  {
    $this->content = $content;

    return $this;
  }

  public function getVote(): ?string
  {
    return $this->vote;
  }

  public function setVote(?string $vote): self
  {
    $this->vote = $vote;

    return $this;
  }

  /**
   * @return mixed
   */
  public function getQuestion()
  {
    return $this->question;
  }

  /**
   * @param mixed $question
   */
  public function setQuestion(Question $question): void
  {
    $this->question = $question;
  }

  public function setVoteCount(int $vote): self
  {
    $this->vote = $vote;

    return $this;
  }

  public function getAuthor(): ?User
  {
      return $this->author;
  }

  public function setAuthor(?User $author): self
  {
      $this->author = $author;

      return $this;
  }
}
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Question:

<?php

namespace App\Entity;

use App\Repository\QuestionRepository;
use Doctrine\ORM\Mapping as ORM;
use Gedmo\Mapping\Annotation as Gedmo;

/**
 * @ORM\Entity(repositoryClass=QuestionRepository::class)
 */
class Question
{
    /**
     * @ORM\Id()
     * @ORM\GeneratedValue()
     * @ORM\Column(type="integer")
     */
    private $id;

    /**
     * @ORM\Column(type="string", length=255)
     */
    private $title;

    /**
     * @Gedmo\Slug(fields={"title"})
     * @ORM\Column(type="string", length=100, unique=true)
     */
    private $slug;

    /**
     * @ORM\Column(type="string", length=255)
     */
    private $questionContent;

    /**
     * @ORM\Column(type="datetime", nullable=true)
     */
    private $publishedAt;

    /**
     * @ORM\ManyToOne(targetEntity=User::class, inversedBy="questions")
     * @ORM\JoinColumn(nullable=false)
     */
    private $author;

    public function getId(): ?int
    {
        return $this->id;
    }

    public function getTitle(): ?string
    {
        return $this->title;
    }

    public function setTitle(string $title): self
    {
        $this->title = $title;

        return $this;
    }

    public function getSlug(): ?string
    {
        return $this->slug;
    }

    public function setSlug(string $slug): self
    {
        $this->slug = $slug;

        return $this;
    }

    public function getQuestionContent(): ?string
    {
        return $this->questionContent;
    }

    public function setQuestionContent(string $questionContent): self
    {
        $this->questionContent = $questionContent;

        return $this;
    }

    public function getPublishedAt(): ?\DateTimeInterface
    {
        return $this->publishedAt;
    }

    public function setPublishedAt(?\DateTimeInterface $publishedAt): self
    {
        $this->publishedAt = $publishedAt;

        return $this;
    }

    public function getAuthor(): ?User
    {
        return $this->author;
    }

    public function setAuthor(?User $author): self
    {
        $this->author = $author;

        return $this;
    }
}
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So I wanted to execute this query

select question_id, count(question_id) as answer_number
from answer
group by question_id;
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in myAnswerRepository so that I can get this data out - how many answers there are for a given question.

When I do this in TablePlus I get the correct results

  public function findNumberOfAnswersForQuestions()
  {
    return $this->getOrCreateQueryBuilder()
      ->select('an.question as question_id, count(an.question) as answer_number')
      ->groupBy('an.question')
      ->getQuery()
      ->getResult();
  }

  private function getOrCreateQueryBuilder(QueryBuilder $qb = null)
  {
    return $qb ?: $this->createQueryBuilder('an');
  }
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  public function findNumberOfAnswersForQuestions()
  {
    return $this->getOrCreateQueryBuilder()
      ->select('IDENTITY(an.question) as question_id, count(an.question) as answer_number')
      ->groupBy('an.question')
      ->getQuery()
      ->getResult();
  }
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IDENTITY(single\_association\_path\_expression [, fieldMapping]) - Retrieve the foreign key column of association of the owning side
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