TYPO3 alter table with Querybuilder - typo3

Question

How can you use the TYPO3 9 Querybuilder to execute an "ALTER TABLE" command?
ALTER TABLE foo
DROP INDEX bar;
This class should be used to execute the query:
use TYPO3\CMS\Core\Database\ConnectionPool;
...
$table = 'foo';
$queryBuilder = GeneralUtility::makeInstance(ConnectionPool::class)->getQueryBuilderForTable($table);
Or is it necessary to instantiate another database object, which e.g. derives from the Doctrine\DBAL\Schema\Schema class.

Answer 1

This should do the Job:
use TYPO3\CMS\Core\Utility\GeneralUtility;
use TYPO3\CMS\Core\Database\ConnectionPool;
// ...
GeneralUtility::makeInstance(ConnectionPool::class)
->getConnectionForTable('foo')
->exec('ALTER TABLE foo DROP INDEX bar;');
The documentation warns about using queries outside repositories:
https://docs.typo3.org/m/typo3/book-extbasefluid/master/en-us/6-Persistence/3-implement-individual-database-queries.html

Answer 2

Give it try, this may be helpful to you. However, I have never tried to Alter table command before (Never required!!)
$connection = $this->objectManager->get(ConnectionPool::class)->getConnectionForTable($table);
$statement = $this->objectManager->get(
\Doctrine\DBAL\Statement::class
'ALTER TABLE foo DROP INDEX bar',
$connection
);
$query = $this->createQuery();
$query->statement($statement);

Answer 3

Another solution would be the usage of the Doctrine Schema Manager for such cases:
use \TYPO3\CMS\Core\Utility\GeneralUtility;
use \TYPO3\CMS\Core\Database\ConnectionPool;
$connection = GeneralUtility::makeInstance(ConnectionPool::class)->getConnectionForTable('foo');
$connection->getSchemaManager()->dropIndex('bar', 'foo');