TYPO3 v8 has reached its end-of-life March 31st, 2020 and is not maintained by the community anymore.

You can order Extended Long Term Support (ELTS) here: TYPO3 ELTS.

Accessing the database

TYPO3 version 8 LTS

The TYPO3 database should always be accessed using the QueryBuilder of Doctrine. The TYPO3\CMS\Core\Database\ConnectionPool class can be used to create a \TYPO3\CMS\Core\Database\Query\QueryBuilder instance:

$queryBuilder = GeneralUtility::makeInstance(ConnectionPool::class)->getQueryBuilderForTable('tablename');

See the Database Access API documentation for details.

For TYPO3 versions before 8 LTS

The TYPO3 database should always be accessed through the use of $GLOBALS['TYPO3_DB']. This is the instance of the DatabaseConnection class from typo3/sysext/core/Classes/Database/DatabaseConnection.php.

The same rule applies for accessing non-TYPO3 databases: they should be accessed by using a different instance of the same class. Failing this condition may corrupt the TYPO3 database or prevent access to the TYPO3 database for the rest of the script.