Question

Please provide a simple solution to the following problem in concise PHP type code (just needs to loosely follow PHP type syntax):

We want to be able to output a nested list of items – items in the list can be sub-items of other items in the list. A simple SQL table would have the following fields:

1. itemID – int.
2. item – varchar.
3. subItemOfID – int.

A small subset of data would look something like this:

itemID  item    subItemOfID
1   Item1   0
2   Item2   0
3   Item3   0
4   Item10  1
5   Item11  1
6   Item12  1
7   Item100 4
8   Item101 4
9   Item102 4
10  Item30  3
11  Item31  3
12  Item32  3

The output would need to look something like this (nested lists sorted by item):

•   Item1
    o       Item10
           Item100
           Item101
           Item102
    o       Item11
    o       Item12
•   Item2
•   Item3
    o       Item30
    o       Item31
    o       Item32

I would get this if the SubItemOfID row was in descending order but the previous examples I used had a regex in it on the item which I was always told this was a bad way of doing something with tables because varchars can change. I need help! This is what I have so far:

<?php
$table = array (
'itemID' => array( 
                    1,2,3,4,5,6,7,8,9,10,11,12
                ),
'item' => array(
                    'Item1','Item2','Item3','Item10','Item11','Item12','Item100','Item101','Item102','Item30','Item31','Item32'
                ),
'subItemOfID' => array(
                    0,0,0,1,1,1,4,4,4,3,3,3
                )
                );

foreach($table as $header => $column) {
    foreach($column as $data) {
        if($header == 'item') {
            $fixed = intval(str_replace('Item','',$data));      
            $str_len = strlen($fixed);
            echo '<ul>';
            if($str_len === 1) {
                echo '<li>'.$data.'</li>';
            }
            echo '<ul>';
            if($str_len === 2  ) {
                echo '<li>'.$data.'</li>';              
            }
            echo'<ul>';
            if($str_len ===3) {
                echo '<li>'.$data.'</li>';
            }
            echo '</ul>';
            echo '</ul>';
            echo '</ul>';       
        }
    }
}
?>
enter code here

Answer 1

With this query you can fetch up to 6 lvls of categories:

$sql = "SELECT c1.item AS item,
              IF(c6.item IS NOT NULL, 6,
                  IF(c5.item IS NOT NULL, 5,
                     IF(c4.item IS NOT NULL, 4,
                        IF(c3.item IS NOT NULL, 3,
                           IF(c2.item IS NOT NULL, 2, 1))))) AS lvl,
              if (c6.item IS NOT NULL, CONCAT(c6.itemId, c5.itemId, c4.itemId, c3.itemId, c2.itemId, c1.itemId),
                  IF(c5.item IS NOT NULL, CONCAT(c5.itemId, c4.itemId, c3.itemId, c2.itemId, c1.itemId),
                     IF(c4.item IS NOT NULL, CONCAT(c4.itemId, c3.itemId, c2.itemId, c1.itemId),
                        IF(c3.item IS NOT NULL, CONCAT(c3.itemId, c2.itemId, c1.itemId),
                           IF(c2.item IS NOT NULL, CONCAT(c2.itemId, c1.itemId), c1.itemId))))) AS code,
       FROM categories c1
       LEFT JOIN categories c2 ON c2.itemId = c1.subItemOfID
       LEFT JOIN categories c3 ON c3.itemId = c2.subItemOfID
       LEFT JOIN categories c4 ON c4.itemId = c3.subItemOfID
       LEFT JOIN categories c5 ON c5.itemId = c4.subItemOfID
       LEFT JOIN categories c6 ON c6.itemId = c5.subItemOfID
       GROUP BY c1.itemId
       ORDER BY code";
$q = mysql_query($sql);
while (false !== ($row = mysql_fetch_assoc($q))) {
    echo str_repeat('---', $row['lvl'])
       . $row['title']
       . '<br />';
}

What does it do: selects every category and its parent categories (if exist), then generate code field to sort them.

Sorry, I inattentively read the question.

Here is the solution in php:

$table = array (
    'itemID' => array(
        1,2,3,4,5,6,7,8,9,10,11,12
    ),
    'item' => array(
        'Item1','Item2','Item3','Item10','Item11','Item12','Item100','Item101','Item102','Item30','Item31','Item32'
    ),
    'subItemOfID' => array(
        0,0,0,1,1,1,4,4,4,3,3,3
    )
);
outputChildrenRecursive(0, $table);

/**
 * Outputs child items recursively
 *
 * @param integer $parentItemID Parent item itemID
 * @param array   $table        Table data
 */
function outputChildrenRecursive($parentItemID, array $table)
{
    // Get children
    $children = array();
    foreach ($table['itemID'] as $key => $value) {
        if ($table['subItemOfID'][$key] == $parentItemID) {
            $children[] = $key;
        }
    }

    // Output children and grandchildren
    if (!empty($children)) {
        echo '<ul>';
        foreach ($children as $childKey) {
            echo '<li>';
            echo $table['item'][$childKey];
            // Prevent infinite recursion if itemID equals subItemOfID
            if ($table['itemID'][$childKey] != $table['subItemOfID'][$childKey]) {
                outputChildrenRecursive($table['itemID'][$childKey], $table);
            }
            echo '</li>';
        }
        echo '</ul>';
    }
}