在Mysql表上计数相同的值

Question

I want to count the max value on the table based on single field.

I have a image_count field on my table; that's counts different images not different thumbnails with same image.

For example i have an image named stack.jpg and have three thumbnails in different sizes.

So i have to save that resized images to db with same image_count.

Let's give a count number to that files: 1.

When i upload another image with three thumbnail sizes again; that uploaded and resized images must has the image_count: 2.

So:

ID | Thumbnail |        Image         | count |
-----------------------------------------------
 1 |   Small   |   stack_small.jpg    |   1   |
 2 |   Medium  |   stack_medium.jpg   |   1   |
 3 |   Big     |   stack_big.jpg      |   1   |
 4 |   Small   |   overflw_small.jpg  |   2   |
 5 |   Medium  |   overflw_medium.jpg |   2   |
 6 |   Big     |   overflw_big.jpg    |   2   |
-----------------------------------------------

When i want to add a new image to db, count field has to be "3". Not 7.

I have to group by count i think but i'm using symfony2 with doctrine and when i try to get singleScalarResult with count, it is throwing exception.

My Code:

public function countImages($entity_id, $gallery_id)
{
    $em = $this->getEntityManager();
    $qb = $em->createQueryBuilder();

    $count = $qb
        ->select('COUNT(i)')
        ->from('CSGalleryBundle:GalleryImage', 'i')
        ->leftJoin('CSGalleryBundle:Gallery', 'g', 'WITH', 'g.id = i.gallery_id')
        ->where(
            $qb->expr()->eq('i.foreign_key', $entity_id),
            $qb->expr()->eq('g.id', $gallery_id)
        )
        ->groupBy('i.image_count')
        ->setMaxResults(1)
        ->getQuery()
        ->getSingleScalarResult();

    return $count + 1;
}

Error:

What is the problem here? How can i solve? Is there any better way to do it?

Thank you!

Answer 1

You can change query with below for basic solve:

$count = $qb
   ->select('i')
   ->from('CSGalleryBundle:GalleryImage', 'i')
   ->leftJoin('CSGalleryBundle:Gallery', 'g', 'WITH', 'g.id = i.gallery_id')
   ->where(
       $qb->expr()->eq('i.foreign_key', $entity_id),
       $qb->expr()->eq('g.id', $gallery_id)
   )
   ->groupBy('i.image_count')
   ->getQuery()
   ->getResult();

return count($count);

Maybe you can review Doctrine Query Builder Documentation for more efficiently resolves.

Answer 2

You are right. You must use Doctrine way for increase performance. You can use this query:

$count = $qb
        ->select('MAX(i.image_count)')
        ->from('CSGalleryBundle:GalleryImage', 'i')
        ->leftJoin('CSGalleryBundle:Gallery', 'g', 'WITH', 'g.id = i.gallery_id')
        ->where(
            $qb->expr()->eq('i.foreign_key', $entity_id),
            $qb->expr()->eq('g.id', $gallery_id)
        )
        ->getQuery()
        ->getSingleScalarResult();

return $count === null ? 1 : $count + 1;

Answer 3

You can use count method with distinct

$count = $qb
   ->select('COUNT(DISTINCT i)')
   ->from('CSGalleryBundle:GalleryImage', 'i')
   ->leftJoin('CSGalleryBundle:Gallery', 'g', 'WITH', 'g.id = i.gallery_id')
   ->where(
       $qb->expr()->eq('i.foreign_key', $entity_id),
       $qb->expr()->eq('g.id', $gallery_id)
   )
   ->groupBy('i.image_count')
   ->getQuery()
   ->getSingleScalarResult();

return $count;

I think it will throw an exception if there is no matched data.

Answer 4

Just an attempt. I haven't check this. Why do you have leftJoin in your code?

$count = $qb
    ->select('MAX(i.count)')
    ->from('CSGalleryBundle:GalleryImage', 'i')
    ->getQuery()
    ->getSingleScalarResult();

return $count + 1;