如何在DELETE QUERY中编写LEFT JOIN？

Will you give me an example of a delete query that use a left join using Doctrine?

It's not possible. See that: http://trac.doctrine-project.org/ticket/2142

You have to use a subquery in the where clause: http://www.doctrine-project.org/documentation/manual/1_2/en/dql-doctrine-query-language:subqueries

Try something like that:

$q = Doctrine_Query::create()
    ->delete('TableB b')
    ->where('b.id NOT IN (SELECT b.id FROM TableB b \
          INNER JOIN b.TableA a WHERE b.date > NOW() AND a.channel_id = 10)')
    ->execute();

Its not necessary to write the query in plain sql, you can still use the QueryBuilder for that:

$entityManager           = $this->getEntityManager();
$queryBuilder            = $entityManager->createQueryBuilder();
$subQueryCityDataSources = $queryBuilder->getEntityManager()->createQueryBuilder()
    ->select('cds')
    ->from(CityDataSource::class, 'cds')
    ->where('cds.dataSource = :dataSource')
;

$queryBuilder->delete($entityClass, 'd');
$queryBuilder->where($queryBuilder->expr()->in('d.cityDataSource', $subQueryCityDataSources->getDQL()));
$queryBuilder->setParameter('dataSource', $dataSource);

$query = $queryBuilder->getQuery();
$query->execute();

This generates this query:

DELETE 
    AppBundle\Entity\ConcreteData\News d 
WHERE 
    d.cityDataSource IN
    (
        SELECT
            cds
        FROM
            AppBundle\Entity\CityDataSource cds
        WHERE
            cds.dataSource = :dataSource
    )

Important note: you have to append all the parameters in the outer query.