Yii2如何返回结果记录数 [ 2.0 版本 ]

那可以这样：

return [
    // ...
    'components' => [
        // ...
        'db' => [
            'class' => 'yii\db\Connection',
            'dsn' => 'mysql:host=localhost;dbname=mydatabase', 
            'username' => 'root',
            'password' => '',
            'charset' => 'utf8',
        ],
//可以配置多个
        'db2' => [
            'class' => 'yii\db\Connection',
            'dsn' => 'mysql:host=localhost;dbname=mydatabase2', 
            'username' => 'root',
            'password' => '',
            'charset' => 'utf8',
        ],
    ],
    // ...
];

然后

$connection = \Yii::$app->db;
$connection2 = \Yii::$app->db2;

然后

//一旦有了连接实例就可以通过yii\db\Command执行 SQL 查询。你拿你需要的连接实例去查就好了
$command = $connection->createCommand('SELECT count(*) FROM post');
$post = $command->queryOne();