Error message after upgrading to 3.5.17 (from 2.11.9)

Question

You must define the following database parameters: database
ee/EllisLab/ExpressionEngine/Service/Database/DBConfig.php:157 

Stack Trace:
        #0 ee/EllisLab/ExpressionEngine/Service/Database/Database.php(151): EllisLab\ExpressionEngine\Service\Database\DBConfig->getGroupConfig()
        #1 ee/EllisLab/ExpressionEngine/Service/Database/Database.php(84): EllisLab\ExpressionEngine\Service\Database\Database->newConnection()
        #2 ee/EllisLab/ExpressionEngine/Service/Database/Database.php(51): EllisLab\ExpressionEngine\Service\Database\Database->getConnection()
        #3 ee/legacy/database/DB.php(48): EllisLab\ExpressionEngine\Service\Database\Database->newQuery()
        #4 ee/legacy/core/Loader.php(381): DB('')
        #5 ee/legacy/libraries/Core.php(107): EE_Loader->database()
        #6 ee/legacy/core/Controller.php(88): EE_Core->bootstrap()
        #7 ee/legacy/core/Controller.php(119): EE_Controller->__construct()
        #8 ee/EllisLab/ExpressionEngine/Core/Core.php(187): CP_Controller->__construct()
        #9 ee/EllisLab/ExpressionEngine/Core/Core.php(94): EllisLab\ExpressionEngine\Core\Core->runController(Array)
        #10 ee/EllisLab/ExpressionEngine/Boot/boot.php(151): EllisLab\ExpressionEngine\Core\Core->run(Object(EllisLab\ExpressionEngine\Core\Request))
        #11 admin.php(143): require_once('...')

Answer 1

Are you absolutely sure you have your DB settings correct in your config.php file? They should have this format in that file:

$config['database'] = array (
    'expressionengine' =>
        array (
            'hostname' => '',
            'username' => '',
            'password' => '',
            'database' => ''
        ),
);

Obviously, fill in the values with your credentials. database should have the name of your schema you installed EE to.