具有聚合函数的行计数 - Row counting with aggregate functions

我在计算所有行时遇到问题。我的问题是：

SELECT info.pid, Name, Addr, Phone, GROUP_CONCAT(URL) as URL
FROM info, images WHERE info.pid = images.pid AND place='$kraj' GROUP BY info.pid

我不能使用mysql_num_rows，因为即使没有结果，group_concat()也会创建一行（空值）。

我尝试将COUNT()放入查询：中

...GROUP_CONCAT(URL) as URL, COUNT(info.pid) as num FROM info...

但它为每个联接计算单独的行。

有什么建议吗？

为什么不过滤掉空值？：

SELECT info.pid, Name, Addr, Phone, GROUP_CONCAT(URL) as URL
  FROM info
  JOIN images
    ON info.pid = images.pid
 WHERE place = ...
   AND URL IS NOT NULL
 GROUP
    BY info.pid
;