PHP/SQL, Reduce number of queries - php

Question

I am querying a large db in php, and I am not doing it near well enough.
I have the code I need, I simple cannot find a good way to compact these statements.
$q = $_GET['q'];
(dbinit)
$query = "SELECT post_id FROM wp_postmeta WHERE meta_key = '_billing_email' AND meta_value = '$q'";
$result = mysql_query($query);
while ($row = mysql_fetch_array($result))
{
$thing = $row['post_id'];
$querys = "SELECT 'meta_value' FROM wp_postmeta WHERE post_id = '$thing' AND meta_key = '_order_number'";
$results = mysql_query($querys);
$rows = mysql_fetch_array($results);
$postid = $rows['meta_value'];
$queryss = "SELECT post_id FROM $table WHERE meta_value = $postid AND meta_key = '_order_number'";
$resultss = mysql_query($query);
$rowss = mysql_fetch_array($result);
$order_id = $rowss['post_id'];
(handling)
}
I am wondering if there is a more efficient way to do these queries, or perhaps have them in one query?

Answer 1

Not sure where $table comes from.
But this JOIN attempt should work:
$q = $_GET['q'];
// ... dbinit ...
$query = "SELECT wpp.post_id,
wpp1.meta_value as orderNumber,
wpp2.post_id as orderId
FROM wp_postmeta wpp
LEFT JOIN wp_postmeta wpp1
ON wpp1.post_id = wpp.post_id
AND wpp1.meta_key = '_order_number'
LEFT JOIN $table wpp2
ON wpp2.meta_value = wpp1.meta_value
AND wpp2.meta_key = '_order_number'
WHERE wpp.meta_key = '_billing_email'
AND meta_value = '$q'";
$result = mysql_query($query);
while ($row = mysql_fetch_array($result)) {
(handling)
}
As you can see you can get
$thing = $row['post_id'];
$order_id = $row['orderId'];
inside the loop if needed.