如何计算 SQL 中最常见的值

Question

目前我有以下代码：

$forummost = mysql_query("
 SELECT door, 
 COUNT(door) AS doorCount 
 FROM forum_posts 
 GROUP BY door 
 ORDER BY COUNT(door) 
 DESC
");
$forummostc = mysql_num_rows($forummost);
$forummostf = mysql_fetch_assoc($forummost);

有人可以解释为什么mysql_num_rows（$forummost）不起作用吗？

提前感谢！

Answer 1

GROUP BY 在 mysql 中仅选择该列的不同值。如前所述，在您的情况下，它会选择与不同door值一样多的行。

Answer 2

mysql_num_rows计算查询返回的行数。您的查询what is the count for each door因此每个门只返回一行。

Answer 3

试试这个，我测试过，它有效。.

<?php 
$link = mysql_connect('localhost','root',''); 
if (!$link) 
{ 
    die('Could not connect to MySQL: ' . mysql_error()); 
} 
echo 'Connection OK'."</br>"; 

$forummost = mysql_query("
    SELECT door, 
COUNT(door) AS doorCount 
FROM forum_posts 
GROUP BY door 
ORDER BY COUNT(door) 
DESC
");

$forummostc = mysql_num_rows($forummost);
if ($forummostc == 0) {
    echo "No rows found, nothing to print so am exiting";
    exit;
}
while ($row = mysql_fetch_assoc($forummost)) {
    echo $row["door"];
    echo $row["doorCount"];
}
mysql_free_result($forummost);
mysql_close($link); 
?>