


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 <p><strong>Explanation</strong></p><p>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.</p><p><strong>Alternative Syntax</strong></p><p>Alternatively, you can use the query builder syntax, which offers an intuitive and flexible way to construct queries:</p><pre class="brush:php;toolbar:false">$qb = $em->createQueryBuilder(); $qb->select('a') ->from('AppBundle:Score', 'a') ->leftJoin('AppBundle:Score', 'b', 'WITH', 'a.name = b.name AND a.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.
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