Update two ID's at once SQL - PHP - php

Question

I have a table that's PK is an int field.
My problem is I need to swap two of the values round.
This is my current code:
$newId = (int)$id; $newId = $newId - 1;
$result = mysql_query("UPDATE homeScroller SET id = '$newId' WHERE id = '$id'") or die('error '.mysql_error());
$result2 = mysql_query("UPDATE homeScroller SET id = '$id ' WHERE id = '$newId'") or die('error '.mysql_error());
The table contains at max 3 rows that contain info for an slideshow on the frontpage of the website. The frontpage orders them by their IDs. So to change the order I need to edit the ID's.

Answer 1

The table contains at max 3 rows that contain info for an slideshow on the frontpage of the website. The frontpage orders them by their IDs. So to change the order I need to edit the ID's.
If that's the case, then your application/database is poorly architect-ed, and you need to re-think your database design before you go any further.
Primary keys should be immutable, i.e.: they should never change. What you're talking about doing is changing primary keys.
Fix your application/database, and you won't have this problem. Are you sure you shouldn't just be adding a new field 'sort_order' and ORDER BY sort_order instead or ordering by the ID field?

Answer 2

Assign one with a temporary id (0, because auto_increment usually starts at 1, so 0 should be unused):
$result = mysql_query("UPDATE homeScroller SET id = 0 WHERE id = '$id'");
$result = mysql_query("UPDATE homeScroller SET id = '$id ' WHERE id = '$newId'");
$result = mysql_query("UPDATE homeScroller SET id = '$newId ' WHERE id = 0");
IMPORTANT: However, you shouldn't rely on the primary key for ordering results, if you want to be able to change the order easily. Add a sequence column and sort by that instead.

Answer 3

UPDATE homeScroller
SET id = CASE id WHEN $id THEN $newid ELSE $id END
WHERE id IN ($id, $newid)

Answer 4

Do not use PK for this need.
If you can add timestamp field (shown_at) to this table, do it!
if cant, so update all PKs imultaneously. Just increment them.
For example: suppose we have such strings:
1 photo1
3 myphoto
5 somephoto
than use modulo 3.
1%3 = 1
3%3 = 0
5%3 = 2
increment all records
2 photo1
4 myphoto
5 somephoto
2%3 = 2
4%3 = 1
6%3 = 0
So u can use modulo and increment ids