Database Exception – yii\db\Exception

                } else {
                    $this->pdoStatement->execute();
                }
                break;
            } catch (\Exception $e) {
                $rawSql = $rawSql ?: $this->getRawSql();
                $e = $this->db->getSchema()->convertException($e, $rawSql);
                if ($this->_retryHandler === null || !call_user_func($this->_retryHandler, $e, $attempt)) {
                    throw $e;
                }
            }
        }
    }

 
        $this->prepare(true);
 
        try {
            $profile and Yii::beginProfile($rawSql, 'yii\db\Command::query');
 
            $this->internalExecute($rawSql);
 
            if ($method === '') {
                $result = new DataReader($this);
            } else {
                if ($fetchMode === null) {
                    $fetchMode = $this->fetchMode;

     * @return string|int|null|false the value of the first column in the first row of the query result.
     * False is returned if there is no value.
     * @throws Exception execution failed
     */
    public function queryScalar()
    {
        $result = $this->queryInternal('fetchColumn', 0);
        if (is_resource($result) && get_resource_type($result) === 'stream') {
            return stream_get_contents($result);
        }
 
        return $result;
    }

        $command = (new self())
            ->select([$selectExpression])
            ->from(['c' => $this])
            ->createCommand($db);
        $this->setCommandCache($command);
 
        return $command->queryScalar();
    }
 
    /**
     * Returns table names used in [[from]] indexed by aliases.
     * Both aliases and names are enclosed into {{ and }}.
     * @return string[] table names indexed by aliases

        $modelClass = $this->modelClass;
        if ($db === null) {
            $db = $modelClass::getDb();
        }
 
        if ($this->sql === null) {
            return parent::queryScalar($selectExpression, $db);
        }
 
        $command = (new Query())->select([$selectExpression])
            ->from(['c' => "({$this->sql})"])
            ->params($this->params)
            ->createCommand($db);

    public function count($q = '*', $db = null)
    {
        if ($this->emulateExecution) {
            return 0;
        }
 
        return $this->queryScalar("COUNT($q)", $db);
    }
 
    /**
     * Returns the sum of the specified column values.
     * @param string $q the column name or expression.
     * Make sure you properly [quote](guide:db-dao#quoting-table-and-column-names) column names in the expression.

        $args = $this->controller->bindActionParams($this, $params);
        Yii::debug('Running action: ' . get_class($this->controller) . '::' . $this->actionMethod . '()', __METHOD__);
        if (Yii::$app->requestedParams === null) {
            Yii::$app->requestedParams = $args;
        }
 
        return call_user_func_array([$this->controller, $this->actionMethod], $args);
    }
}

        }
 
        $result = null;
 
        if ($runAction && $this->beforeAction($action)) {
            // run the action
            $result = $action->runWithParams($params);
 
            $result = $this->afterAction($action, $result);
 
            // call afterAction on modules
            foreach ($modules as $module) {
                /* @var $module Module */

        $parts = $this->createController($route);
        if (is_array($parts)) {
            /* @var $controller Controller */
            list($controller, $actionID) = $parts;
            $oldController = Yii::$app->controller;
            Yii::$app->controller = $controller;
            $result = $controller->runAction($actionID, $params);
            if ($oldController !== null) {
                Yii::$app->controller = $oldController;
            }
 
            return $result;
        }

            $params = $this->catchAll;
            unset($params[0]);
        }
        try {
            Yii::debug("Route requested: '$route'", __METHOD__);
            $this->requestedRoute = $route;
            $result = $this->runAction($route, $params);
            if ($result instanceof Response) {
                return $result;
            }
 
            $response = $this->getResponse();
            if ($result !== null) {

    {
        try {
            $this->state = self::STATE_BEFORE_REQUEST;
            $this->trigger(self::EVENT_BEFORE_REQUEST);
 
            $this->state = self::STATE_HANDLING_REQUEST;
            $response = $this->handleRequest($this->getRequest());
 
            $this->state = self::STATE_AFTER_REQUEST;
            $this->trigger(self::EVENT_AFTER_REQUEST);
 
            $this->state = self::STATE_SENDING_RESPONSE;
            $response->send();