Variables mysql y php

Solo puede tener una consulta a la vez en PHP.

 $query1 = "SELECT count(*) FROM agents INTO @AgentCount"
 $query2="  
  SELECT user_agent_parsed, user_agent_original, COUNT( user_agent_parsed ) AS thecount, 
  COUNT( * ) / ( @AgentCount) AS percentage
  FROM agents
  GROUP BY user_agent_parsed
  ORDER BY thecount DESC LIMIT 50";

ACTUALIZAR

Tengo un DAL que contiene todas mis consultas. Una función típica en mi DAL se ve así:

// These functions are reusable 
  public function getAllRows($table)
  {
    $sql =" SELECT * FROM $table";
    $this->query($sql);
    return $this->query_result;       
  }

Luego, en mi BLL (Business Layer) tengo lo siguiente:

  public function getUserAgents()
  {
      $result = parent::getAllRows();
      $row = mysql_fetch_array($result);
      return $row[0]; // Retrieves the first row

      // Then you take this value and to a second request. Then return the answer / rows.
  }