如何从php

Question

我有一个相当大的firebird数据库，我试图从中获取数据，我使用pdo类，并且这样使用它：

for($i=0; $i < $hours; $i++):
$date = date('H:i:s',strtotime("+$i hour"));
$newdate = date('H:i:s', strtotime($date . "+1 hour"));
$sql = "SELECT count(*) as NUMBER FROM BANDZENDINGEN WHERE FT_TIJD_INGEVOERD BETWEEN '".$date."' AND '".$newdate."' AND FI_GEBRUIKER1='56'";
$count = $dbh->query($sql)->fetchColumn();

endfor;

这很简单，我给出了几个小时，在这个小时中，该查询为用户计算了导入次数。示例：

 $hours = 4;


 SELECT count(*) as NUMBER FROM BANDZENDINGEN WHERE FT_TIJD_INGEVOERD BETWEEN '08:40:57' AND '09:40:57' AND FI_GEBRUIKER1='56'
 SELECT count(*) as NUMBER FROM BANDZENDINGEN WHERE FT_TIJD_INGEVOERD BETWEEN '09:40:57' AND '10:40:57' AND FI_GEBRUIKER1='56'
 SELECT count(*) as NUMBER FROM BANDZENDINGEN WHERE FT_TIJD_INGEVOERD BETWEEN '10:40:57' AND '11:40:57' AND FI_GEBRUIKER1='56'
 SELECT count(*) as NUMBER FROM BANDZENDINGEN WHERE FT_TIJD_INGEVOERD BETWEEN '11:40:57' AND '12:40:57' AND FI_GEBRUIKER1='56'

问题是$ count = $ dbh-> query（$ sql）-> fetchColumn（）;给我一个错误503-服务不可用！如果我在数据库内执行此查询（RazorSql），则只需19秒即可完成。我究竟做错了什么？请帮忙。