先创建连接对象

$connection = new \yii\db\Connection([
    'dsn' => $dsn,
     'username' => $username,
     'password' => $password,
]);
$connection->open();

查询返回多行：

$command = $connection->createCommand('SELECT * FROM post');
$posts = $command->queryAll();

返回单行：

$command = $connection->createCommand('SELECT * FROM post WHERE id=1');
$post = $command->queryOne();

查询多行单值：

$command = $connection->createCommand('SELECT title FROM post');
$titles = $command->queryColumn();

查询标量值/计算值：

$command = $connection->createCommand('SELECT COUNT(*) FROM post');
$postCount = $command->queryScalar();

要养成先查文档的习惯：
http://www.yiichina.com/doc/guide/2.0/db-dao

我创建的时候 这两个时间一起插入数据库没有问题 但是当我修改的时候 两个时间没有变化
如果我同时给这两个时间加上值 update_at=time()和created_at=time() 数据库同时两个时间都更新了 我只想让update_at一个时间更新 怎么做
model

public function behaviors()
	{
	    return [
	        [
	            'class' => TimestampBehavior::className(),
	            'attributes' => [
	              ActiveRecord::EVENT_BEFORE_INSERT => ['created_at', 'updated_at'],
	              ActiveRecord::EVENT_BEFORE_UPDATE => ['updated_at'],
				],
	            'value' => new Expression('NOW()'),
	        ],
	    ];
	}

controller

                        $post['updated_at']=date('Y-m-d H:i:s',time());
                        $post['created_at']=date('Y-m-d H:i:s',time());
                        $news->attributes = $post;
			$news->save();
			if ($news->hasErrors())
			{
				return $this->redirectMessage($news->getError());
			}
			return $this->redirect('/news');

我创建的时候 这两个时间一起插入数据库没有问题 但是当我修改的时候 两个时间没有变化
如果我同时给这两个时间加上值 update_at=time()和created_at=time() 数据库同时两个时间都更新了 我只想让update_at一个时间更新 怎么做
model

public function behaviors()
	{
	    return [
	        [
	            'class' => TimestampBehavior::className(),
	            'attributes' => [
	              ActiveRecord::EVENT_BEFORE_INSERT => ['created_at', 'updated_at'],
	              ActiveRecord::EVENT_BEFORE_UPDATE => ['updated_at'],
				],
	            'value' => new Expression('NOW()'),
	        ],
	    ];
	}

controller

                        $post['updated_at']=date('Y-m-d H:i:s',time());
                        $post['created_at']=date('Y-m-d H:i:s',time());
                        $news->attributes = $post;
			$news->save();
			if ($news->hasErrors())
			{
				return $this->redirectMessage($news->getError());
			}
			return $this->redirect('/news');