yii\db\Connection::getQueryBuilder PHP Method

    public function getQueryBuilder()
    {
        return $this->getSchema()->getQueryBuilder();
    }

 /**
  * Sign emails to claim emails send by CURRENT PROCESS, then signed emails will not be retrieved by other processes.
  *
  * @param bool $signUnassigned Whether to sign email those are not assigned to any server_id (IS NULL).
  * Take effects only when column specified by EmailQueueCommand::$sendByCol exists.
  * @param bool $renewSignature Whether to renew the signature when sign emails every time.
  *
  * @return int The numbers of mails signed this time.
  *
  */
 protected function signEmails($signUnassigned = true, $renewSignature = false)
 {
     $modelClass = $this->_templateModel;
     $where = [$this->signatureAttr => null];
     if ($modelClass->hasAttribute($this->assignedToSvrAttr)) {
         $where = ['and', $where];
         if ($signUnassigned) {
             $where[] = ['or', [$this->assignedToSvrAttr => $this->serverID], [$this->assignedToSvrAttr => null]];
         } else {
             $where[] = [$this->assignedToSvrAttr => $this->serverID];
         }
     } elseif (!$signUnassigned) {
         $msg = "Cannot find any entries to sign, while 'signUnassigned' is false ";
         $msg .= "and attribute '{$this->assignedToSvrAttr}' is missing in model class.";
         $this->consoleLog($msg, true, Console::FG_YELLOW);
         return 0;
     }
     $cols = [$this->signatureAttr => $this->getSignature($renewSignature)];
     $queryBuilder = $this->_db->getQueryBuilder();
     $sql = $queryBuilder->update($modelClass::tableName(), $cols, $where, $params);
     if ($this->signSize) {
         $sql = $queryBuilder->buildOrderByAndLimit($sql, null, $this->signSize, null);
     }
     return $this->_db->createCommand($sql, $params)->execute();
 }