Query does not do what I want it to do - php

Question

$mpn = $P[0];
$qty = $P[14];
$mysql_connection = mysql_connect('localhost', 'my_db', 'my_pass');
if (!$mysql_connection) {
die('Could not connect to db: ' . mysql_error());
}
mysql_select_db('my_db', $mysql_connection);
$id = mysql_query("SELECT productid FROM my_table_2 WHERE value = '$mpn'");
if (!$id) {
return("XXX-99999");
}
mysql_select_db('my_db', $mysql_connection);
$sku = mysql_query("SELECT productcode FROM my_table WHERE productid = $id");
if (!$sku) {
return("XXX-99999");
}
mysql_select_db('my_db', $mysql_connection);
$qty2 = mysql_query("SELECT avail FROM my_table WHERE productcode = '$sku'");
if (!$qty2) {
return("XXX-99999");
}
if ($qty2 <1 && $qty >0 && $qty2 != $qty) {
return($sku);
}
else {
return("XXX-99999");
}
I'm trying to match Manufacturers part numbers from Product feed and database to accomplish putting out of stock products from main source to secondary source. It does not work. What I am doing wrong?
This has been edited to try and explain the situation more clearly. First this is going into an app and is a snippit to be used by that app. Hence mysql instead of mysqli. The variable $mpn in the first query comes from $mpn = ($P[0]); at the top. It is in a feed and not in the database as a column. $sku in the second query comes from the result of the first query and is not in the database as a column. The app loops this code for each line of the feed.
The above fails to achieve the desired effect of providing the last argument even though I know it for sure should (I set it up). Given the new explaination can somebody help?
$mpn = ($P[0]);
$qty = ($P[14]);
$mysql_connection = mysql_connect('localhost', 'user', 'pass' );
if (!$mysql_connection) {
die('Could not connect to db: ' . mysql_error());
}
mysql_select_db('db', $mysql_connection);
$tmp1 = mysql_query("SELECT productcode FROM table1 WHERE mpn != '' && mpn = '$mpn'")or die(mysql_error());
$row1 = mysql_fetch_array($tmp1, MYSQL_BOTH);
$sku = $row1[0];
$tmp2 = mysql_query("SELECT avail FROM table1 WHERE productcode = '$sku'")or die(mysql_error());
$row2 = mysql_fetch_array($tmp2, MYSQL_NUM);
$qty2 = $row2[0];
if ($qty2 <=0 && $qty >0) {
return($sku);
}
else {
return("XXX-99999");
}

Answer 1

You have to fetch the data after mysql_query(look into mysqli instead) using mysql_fetch_array. After fetching assign $row1 = mysql_fetch_array($id); and then you can call the row and column name $row1['productid'];. You also do not need to open assign the database before every call. You can only do it once before running the queries and then run mysql_close($mysql_connection)
$mpn = $P[0];
$qty = $P[14];
$mysql_connection = mysql_connect('localhost', 'my_db', 'my_pass');
if (!$mysql_connection) {
die('Could not connect to db: ' . mysql_error());
}
mysql_select_db('my_db', $mysql_connection);
$id = mysql_query("SELECT productid FROM my_table_2 WHERE value = '$mpn'");
$row1 = mysql_fetch_array($id);
if (!$id) { return("XXX-99999");
}
$sku = mysql_query("SELECT productcode FROM my_table WHERE productid = $row1['productid']");
$row2 = mysql_fetch_array($sku);
if (!$sku) { return("XXX-99999");
}
$qty2 = mysql_query("SELECT avail FROM my_table WHERE productcode = '$row2['productcode']'");
$row3 = mysql_fetch_array($qty2);
if (!$qty2) { return("XXX-99999");
}
if ($row3['avail'] <1 && $qty >0 && $row3['avail'] != $qty) { return($row['productcode']);
}
else {return("XXX-99999");
}
mysql_close($mysql_connection);
This should give you more or less an idea. Use as reference: http://www.php.net/manual/en/function.mysql-connect.php

Answer 2

Here:
$sku = mysql_query("SELECT productcode FROM my_table WHERE productid = $id");
I think it should look like:
$sku = mysql_query("SELECT productcode FROM my_table WHERE productid = '$id' ");