First, we need to create a simple database test
<?php
$link = mysqli_connect('localhost','username','password','test');
mysqli_set_charset($link, "utf8");
if (!$link) {
die("连接失败:".mysqli_connect_error());
}
?>Create a new table class and set 3 fields
Sort id int type.
Category name title varchar type.
Classification pid int type.
A table similar to the following:
Idea:
Define a custom function get_str, set the parent class pid = 0, use SQL The statement queries out its subclasses, Place the queried subclasses into $result
Use a while loop to get out the subclasses, and create an output pattern by constructing a string , call the custom function get_str, pass the id of the subclass into the custom function,
and then continue to query the next level.
<?php
function get_str($id = 0) {
global $str;
global $link; //global 关键词用于访问函数内的全局变量。
$sql = "select id,title from class where pid= $id";
$result = mysqli_query($link,$sql);//查询pid的子类的分类
if($result){//如果有子类
$str .= '<ul>';
while ($row = mysqli_fetch_array($result)) { //循环记录集
$str .= "<li>" . $row['id'] . "--" . $row['title'] . "</li>"; //构建字符串
get_str($row['id']); //调用get_str()，将记录集中的id参数传入函数中，继续查询下级
}
$str .= '</ul>';
}
return $str;
}
echo get_str(0);
?>The output is similar to:
