Question

I am having difficulty updating a range of columns using mysql. My overall goal is to give the user the ability to change a list item’s position and to have all of the other list items shift position to accommodate for the change. So say you have a range of numbers, 1-6 and you would like to move the item in position 2 to position 4 and have each item compensate for the change while each occupying only a single position number. I have been working on this for a few hours now and I am getting too tired to think straight. I am still very much a newbie with mysql but I have almost finished making my first cms except for this last annoying tidbit.

The code in question is:

$newposition = $_POST['position'];
$oldposition = $_GET['oldposition'];
$id = $_GET['id'];

while ($work = mysql_fetch_array($workset)) {

if ($newposition>$oldposition) {
    mysql_query('UPDATE work SET position=position-1 WHERE position<='.$newposition.' AND position>'.$oldposition.'');
    mysql_query('UPDATE work SET position='.$newposition.' WHERE id='.$id.'');
}
elseif 
($newposition<$oldposition) {
    mysql_query('UPDATE work SET position=position+1 WHERE position<'.$oldposition.' AND position<='.$newposition.'');
    mysql_query('UPDATE work SET position='.$newposition.' WHERE id='.$id.'');
}
elseif 
($newposition==$oldposition) {
    echo 'same value!  ';
}
}

It creates the requested position change correctly but all of the other numbers in the range get changed to an incorrect value. It is probably a simple mistake..

Answer 1

So, I came up with a solution for anyone that is interested. It isn’t the cleanest, but it appears to have worked..

if ($newposition>$oldposition) {
    for ($i=$oldposition+1; $i<=$newposition; $i++) {
        $workset = mysql_query('SELECT * FROM work WHERE position='.$i.' LIMIT 1', $connection);
        while ($work = mysql_fetch_array($workset)) {
            mysql_query('UPDATE work SET position='.$i.'-1 WHERE position='.$i.'');
            mysql_query('UPDATE work SET position='.$newposition.' WHERE id='.$id.'');
        }
    }
}
elseif 
($newposition<$oldposition) {
    for ($i=$oldposition-1; $i>=$newposition; $i--) {
        $workset = mysql_query('SELECT * FROM work WHERE position='.$i.' LIMIT 1', $connection);
        while ($work = mysql_fetch_array($workset)) {
            mysql_query('UPDATE work SET position='.$i.'+1 WHERE position='.$i.'');
            mysql_query('UPDATE work SET position='.$newposition.' WHERE id='.$id.'');
        }
    }
}
elseif 
($newposition==$oldposition) {
}