了解PHP / mysql中的递归

Question

I am trying to create and understand recursion in php/mysql

my database looks something like the following

id | woid | parent | name
-------------------------------
1  | 1111 | 0      | pdf
2  | 1111 | 0      | docs
3  | 2222 | 0      | pdf
4  | 2222 | 0      | docs
5  | 3333 | 0      | pdf
6  | 1111 | 2      | folder1
7  | 2222 | 4      | folder3
8  | 3333 | 5      | folder

I would like to have it where if there are tons and tons of parent folders, it will be able to go through all of them. how do i go about doing this.

Answer 1

In order to get SQL to return a more tree-like structure would actually be pretty difficult. Instead, it probably makes more sense (and you'd have a LOT more control over your output) to reorganize the SQL results using PHP.

SELECT id, woid, parent, name FROM files ORDER by parent ASC;

This will get us everything. Then we iterate through the resultset, storing the result into an array keyed by parent.

$folders = array();
foreach ($resultset AS $row) {
    $row['id'] = (int)$row['id'];
    $row['parent'] = (int)$row['parent'];
    if (!$folders[$row['parent']]) $folders[$row['parent']] = array();
    $folders[$row['parent']][] = $row;
}

Then we can output this array recursively:

function buildTree($inputArray, $parent = 0) {
    $return = array();
    foreach ($inputArray[$parent] AS $key => $row) {
        if ($inputArray[$row['id']]) {
            $row['children'] = buildTree($inputArray, $row['id']);
        }
        $return[] = $row;
    }
    return $return;
}

$myStuff = buildTree($folders);

Answer 2

If you are looking for an efficient way to find all parent nodes (or the super parent node), given a node deep down in your hierarchy, you are entering the realm of graph theory, which comes with many own challenges, especially when the structure of your graph is represented in a single table such as in your own case.

Check out this resource for a good overview: http://www.artfulsoftware.com/mysqlbook/sampler/mysqled1ch20.html