Xtykutl

used contains a list of used items. I don't want the item to be used again if it was one of the last 10 items used.

From some googling, it seems like I need a subquery but can't get it to work. Here is what I tried so far

$check = mysqli_query($db, 'SELECT `id` 

                            FROM (

                                SELECT `id` 

                                FROM `used` 

                                ORDER BY `id` DESC 

                                LIMIT 10) 

                            WHERE `item` = ' . $id);

Before this I was using the following

$check = mysqli_query($db, 'SELECT `id` 

                            FROM `used` 

                            WHERE `item` = ' . $id . ' 

                            ORDER BY `id` DESC 

                            LIMIT 10);

However, seems like that was only limiting the results by 10, so would always return true if an item had been used, even outside of the last 10

It sounds like you want to check if the item $id was in the last 10 items in the used table. This query should do that:

$check = mysqli_query($db, "SELECT $id NOT IN (SELECT item 

                                               FROM used 

                                               ORDER BY id DESC 

                                               LIMIT 10)");

This query will return 1 if the value of $id was not in the last 10 values of item in the used table, or 0 otherwise.

For versions of MySQL which don't support LIMIT in IN subqueries, you can use a LEFT JOIN as in this query which will return the same result:

SELECT IF(b.item IS NULL, 1, 0) 

FROM used a 

LEFT JOIN (SELECT item 

           FROM used 

           ORDER BY id DESC LIMIT 10) b ON b.item = a.item 

WHERE a.item = $id 

You can do it with a JOIN:

$check = mysqli_query($db, 'SELECT u.id

FROM used AS u

JOIN (

   SELECT id

   FROM used

  ORDER BY id DESC LIMIT 10) AS ub

USING (id)

WHERE item = ' . $id);

This works if your version does not support 'LIMIT & IN/ALL/ANY/SOME subquery":

$check = mysqli_query($db, 'SELECT `item` FROM

                    (SELECT `item` 

                    FROM `used` 

                    ORDER BY `id` DESC 

                    LIMIT 10) as useditems

                    WHERE `item` = ' . $id );