mysql Count Distinct 并使用 php 得到结果

Question

I have a mysql query like this:

$topicreplycount = mysql_query('SELECT COUNT(DISTINCT post_msg_id) FROM phpbb_attachments WHERE topic_id = '.$row['topic_id'].' AND post_msg_id < '.$row['post_msg_id']);

and hope to get the result using something like this:

$topicreplycount = mysql_result($topicreplycount);

so lets say there are 4 post_msg_ids like this in the table:

2956 2957 2957 2958

and the current $row['post_msg_id'] is 2958, there are 3 post_msg_ids that are less than the one I am comparing it to, and only 2 Distinct post_msg_ids since two of them are the same, I am expecting "2" to be returned

but it doesn't seem to work, am I doing this correctly? I am not getting anything returned in the $topicreplycount variable at all using this method

I am pretty sure usign mysql_result($topicreplycount) must be wrong but don't know what to use instead

Answer 1

Try this:

$sql = mysql_query('SELECT COUNT(DISTINCT post_msg_id) AS num_topics FROM phpbb_attachments WHERE topic_id = '.$row['topic_id'].' AND post_msg_id < '.$row['post_msg_id']);
$result = mysql_result($sql);
$row = mysql_fetch_array($result) or die(mysql_error());
echo $row['num_topics'];

Answer 2

Using mysql_result you need to specify at least the row number so

$topicreplycount = mysql_result($topicreplycount,0);

should work. As there will only ever be one result returned because you used the COUNT() function this will be fine.

However, it is recommended NOT to use the mysql_ family of functions. They are effectively deprecated (not officially but even the PHP docs recommends not to use them). You should switch to mysqli_ or, perhaps better still, PDO.