Question

Im trying to come up with some code to check whether or not a user owns a list of items. The list of items can be any length but will probably be no more than 5.

There are 2 tables involved here: qrequirements and inventory.

I’ve got as far as running a loop to check a user has each item, but I’m stuck on how to record the result of the ownership of each item and how this can be communicated to the user afterwards.

I might be going about all this the wrong way and maybe there’s a simpler way, I don’t know.

Any help would be great. Here’s my code so far:

<?php

// Get the list of required items
$result = mysql_query("select * from qrequirements where qid='2'");
// This might return E.G:
// item1 = '32'
// item2 = '24'
// item3 = '15'

// Loop through each item to check the user has it
while ($row = mysql_fetch_array($result)) {
    $itemid = $row["itemid"];
    $check_inv = mysql_query("select * from inventory where userid='$userid' AND item = $itemid");
    $num_rows = mysql_num_rows($check_inv);
    if($num_rows>=1){
        // Something in here to confirm the item is owned by the user, while we check the others
    }else{
        echo "You do not have this item";
    }
}

// Notify the user if they have all items required

?>

Answer 1

Determining the items that a user needs but does not have can be solved by a single query. The below query should accomplish that task.

SELECT * FROM qrequirements t1
 WHERE t1.quid = '2'
   AND NOT EXISTS ( SELECT 1 FROM inventory t2
                 WHERE t1.item = t2.item
                   AND t2.userid = '$userid')

If you also need to know which items the user does have then this similar query will accomplish that additional task.

SELECT * FROM qrequirements t1
 WHERE t1.quid = '2'
   AND EXISTS ( SELECT 1 FROM inventory t2
                 WHERE t1.item = t2.item
                   AND t2.userid = '$userid')

Another useful query is one that would return the required items and an indicator of whether the user has that item. The item_count will be 0 if the user does not have the item and greater than 0 if the user does have the item.

SELECT t1.*, (SELECT count(*) FROM inventory t2
               WHERE t1.item = t2.item
                 AND t2.userid = '$userid') as item_count
 FROM qrequirements t1
WHERE t1.quid = '2'