WCF::handleException() Unhandled exception: Undefined class constant 'MYSQL_ATTR_INIT_COMMAND'

#0 /var/www/vhosts/big-game-board.net/httpdocs/wbb4/wcf/lib/system/database/Database.class.php(107): wcf\system\database\MySQLDatabase->connect()
#1 /var/www/vhosts/big-game-board.net/httpdocs/wbb4/wcf/lib/system/WCF.class.php(324): wcf\system\database\Database->__construct('localhost', 'bigwbb4', 'htD*298x', 'big-wbb4', 0)
#2 /var/www/vhosts/big-game-board.net/httpdocs/wbb4/wcf/lib/system/WCF.class.php(141): wcf\system\WCF->initDB()
#3 /var/www/vhosts/big-game-board.net/httpdocs/wbb4/wcf/global.php(25): wcf\system\WCF->__construct()
#4 /var/www/vhosts/big-game-board.net/httpdocs/wbb4/global.php(13): require_once('/var/www/vhosts...')
#5 /var/www/vhosts/big-game-board.net/httpdocs/wbb4/index.php(9): require_once('/var/www/vhosts...')
#6 {main}