Doctrine Query Language get Max/Latest Row Per Group - php

Question

I am trying and failing to translate my relatively simple SQL statement into one that will work within Doctrine.
This is the SQL statement, which works as required when run against my database:
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
Here's the DQL attempt thus far:
$kb = $em->createQuery(
"SELECT a
FROM ShmupBundle:Score a
INNER JOIN a.name ShmupBundle:Score b WITH a.score = b.score AND a.name = b.name GROUP BY b.name
WHERE a.platform='keyboard'
GROUP BY a.name
ORDER BY b.score DESC, a.dateCreated DESC"
);
Which is currently giving this error:
[Semantical Error] line 0, col 73 near 'ShmupBundle:Score': Error: Class ShmupBundle\Entity\Score has no association named name
The table itself is pretty simple:
id, name, score, platform, dateCreated
There are multiple entries with the same name, but different scores. I want to show only the "high score" per name. I've been trying on and off for a day or two now, with no luck. Can anyone point me in the right direction?

Answer 1

The query you are trying to do with doctrine is related to greatest-n-per-group. To use a sub query and then join with main query get things complicated to handle with doctrine. So below is the rewritten SQL version to get the same results without use of any aggregate functions:
SELECT
a.*
FROM
score a
LEFT JOIN score b
ON a.name = b.name
AND a.score < b.score
WHERE b.score IS NULL
ORDER BY a.score DESC
DEMO
To convert above query equivalent to doctrine or DQL is easy, below is the DQL version of above SQL:
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
Or with query builder you can write something like i have tested below with symfony 2.8 using the DEMO Schema
$DM = $this->get( 'Doctrine' )->getManager();
$repo = $DM->getRepository( 'AppBundle\Entity\Score' );
$results = $repo->createQueryBuilder( 'a' )
->select( 'a' )
->leftJoin(
'AppBundle\Entity\Score',
'b',
'WITH',
'a.name = b.name AND a.score < b.score'
)
->where( 'b.score IS NULL' )
->orderBy( 'a.score','DESC' )
->getQuery()
->getResult();
Another idea would be create a view using your query in database and in symfony create an entity put the view name in table annotation and just start calling your entity it will give the results returned by your query but this approach is not recommended just a temporary fix.

Answer 2

Inner Join Statement needs first argument as a table, that is a semantic error in your query.
$kb = $em->createQuery(
"SELECT a
FROM ShmupBundle:Score a
INNER JOIN ShmupBundle:Score b ON a.score = b.score AND a.name = b.name GROUP BY b.name
WHERE a.platform='keyboard'
GROUP BY a.name
ORDER BY b.score DESC, a.dateCreated DESC");

Answer 3

MySQL does not understand the : syntax. If ShmupBundle:Score is supposed to be a database and table, then use .. If Doctrine is supposed to replace it with something, then what does it do with it?
There can be only one GROUP BY clause, and it must be after the WHERE clause. Try removing the GROUP BY b.name.
There is no need to GROUP BY both b.name and a.name since they are equal.

Answer 4

use this
in class
$name = $em->getRepository('AppBundle:BlogPost')->getMaxId();
in repository you can use something like
public function getMaxId()
{
$qb = $this->createQueryBuilder('u');
$qb->select('u, MAX(id) as idMax');
return $qb->getQuery()->getSingleResult();
}
each entity come with some default repository functions either we defined or not
if we wish to add some extra functionality we do write down custom functions in repository class. like i want to add one more function getMaxId i will write down in repository to access this function.
for getting max or min from each group we can do with given query
select * from (select * from mytable order by `Group`, age desc, Person) x group by `Group
this is not good way to fetch max from each group as we need to write down sub query for that.
other than that we have Row_number() function
SELECT sd.* FROM ( SELECT sale_person_id,sale_person_name,no_products_sold,commission_percentage,sales_department,ROW_NUMBER() OVER(PARTITION BY sale_person_id ORDER BY no_products_sold DESC) rowNumber FROM sales_department_details )sd WHERE sd.rowNumber =1;
here you find out all work arounds