PHP uses recursive method to implement infinite classification code

$dbhost = "localhost"; // Database host name
$dbuser = "root"; // Database user name
$dbpd = "123456"; // Database password
$dbname = "test"; //Database name
mysql_connect($dbhost,$dbuser,$dbpd); //Connect to host
mysql_select_db($dbname); //Select database
mysql_query("SET NAMES 'utf8'");
 display_tree("├",0);
function display_tree($tag,$classid) {
$result = mysql_query("
SELECT *
FROM ylmf_class
WHERE parentid = '" . $classid . "'
;"
) ;
while ($row = mysql_fetch_array($result)) {
//Indent the node name
echo $tag.$row['classname'] . "";
//Call this again The function displays the child nodes of the child node
display_tree($tag."─┴",$row['id']);
}
}
?>

Remarks:Use recursion This method will be inefficient for a large number of sub-columns. Some mature CMS systems use the production array method to improve efficiency.