Mysql 左联接后从表中获取列

我必须编辑此查询：

$q="select *, (select count(participant_id) 
                from event_tables_seats 
                left join participants on participants.id=event_tables_seats.participant_id 
                where table_id=event_tables.id and participants.status='Active') as participants_in_tables 
    from event_tables 
    where event_id=?";

我的目标是从参与者表中选择列，例如participants.first\u name和participants.last\u name。这是我写的excel导出函数：

    public function export($event_id) 
    {   
    $data = $this->Jot_model->getTablesForEvent($event_id);


    $filename = "table_data_$event_id.xls";

    header("Content-Disposition: attachment; filename=\"$filename\"");
    header("Content-Type: application/vnd.ms-excel");

      $flag = false;
      foreach($data as $row) 
      {
        if (!$flag) 
        {
          echo implode("\t", array_keys($row)) . "\r\n";
          $flag = true;
        }
        echo implode("\t", array_values($row)) . "\r\n";
      }
      exit;
      } 

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使用联接而不是相关子查询

SELECT e.*, p.first_name, p.last_name
FROM event_tables AS e
LEFT JOIN event_tables_seats AS s ON e.id = s.table_id
LEFT JOIN participants AS p ON p.id = s.participant_id
WHERE e.event_id = ?