How to Retrieve the Maximum/Latest Record Per Group Using Doctrine Query Language (DQL)?

Doctrine Query Language: Retrieving Maximum/Latest Record Per Group

Doctrine Query Language (DQL) offers powerful capabilities for retrieving data from databases. One common task is obtaining the maximum or latest row for each group in a dataset.

Translating SQL to DQL

In your case, you're struggling to translate the following SQL statement to DQL:

SELECT a.*
FROM score a
INNER JOIN (
  SELECT name, MAX(score) AS highest
  FROM score
  GROUP BY name
) b
ON a.score = b.highest AND a.name = b.name
GROUP BY name
ORDER BY b.highest DESC, a.dateCreated DESC

This query aims to find the highest score for each name, along with other columns, and order the results by score and then by date created.

DQL Equivalent

To achieve the same functionality in DQL, you can use the following query:

SELECT a
FROM AppBundle\Entity\Score a
LEFT JOIN AppBundle\Entity\Score b
WITH a.name = b.name
AND a.score < b.score
WHERE b.score IS NULL
ORDER BY a.score DESC, a.dateCreated DESC

Explanation

This DQL query utilizes a left join to compare the current row (a) with rows having the same name (b) with higher scores. If there's no row with a higher score for a given name, b.score will be NULL, which is used to filter the results.

Alternative Syntax

Alternatively, you can use the query builder syntax, which offers an intuitive and flexible way to construct queries:

$qb = $em->createQueryBuilder();
$qb->select('a')
   ->from('AppBundle:Score', 'a')
   ->leftJoin('AppBundle:Score', 'b', 'WITH', 'a.name = b.name AND a.score < b.score')
   ->where('b.score IS NULL')
   ->orderBy('a.score', 'DESC')
   ->orderBy('a.dateCreated', 'DESC');

$results = $qb->getQuery()->getResult();

Additional Considerations

For performance optimization, consider creating an index on the score column and on the combination of name and score columns.

The above is the detailed content of How to Retrieve the Maximum/Latest Record Per Group Using Doctrine Query Language (DQL)?. For more information, please follow other related articles on the PHP Chinese website!