Question

So I’m trying to integrate a bit of WordPress with a backend. Their MySQL schema isn’t too great, especially when you add in Woocommerce.

I’ve come up with the following query:

SELECT wp.* 
FROM   wp_postmeta wp
       INNER JOIN (SELECT post_id 
                   FROM   wp_postmeta
                   WHERE  ( `meta_key` = '_shipping_method' 
                            AND `meta_value` = 'free_shipping' ) 
                           OR ( `meta_key` = '_order_items' 
                                AND `meta_value` LIKE '%search%' )) a 
               ON a.post_id = wp.post_id 
ORDER  BY wp.post_id DESC

To be run on this table https://i.stack.imgur.com/qMHQp.jpg to select the right things for certain people.

Now when I var_dump this in PHP it comes out like so (truncated) – http://pastebin.com/WR3byT8k

Is there any way I can map this properly to an array so that I can use something simple like:

echo $content['_billing_first_name']; 
echo $content['_billing_last_name'];

Which would output:
John
Citizen

Keep in mind all the content is dynamic, so I can’t just use row numbers.

Answer 1

If you have a fixed set of meta keys you need to retrieve (not necessarily a fixed order), you can do it in the query itself by using a technique similar to a pivot table.

SELECT 
  post_id,
  MAX(CASE WHEN meta_key = '_billing_first_name' THEN meta_value ELSE NULL END) AS _billing_first_name,
  MAX(CASE WHEN meta_key = '_billing_last_name' THEN meta_value ELSE NULL END) AS _billing_last_name,
  MAX(CASE WHEN meta_key = '_some_other_attribute' THEN meta_value ELSE NULL END) AS _some_other_attribute,
  MAX(CASE WHEN meta_key = '_another_attribute' THEN meta_value ELSE NULL END) AS _another_attribute,
  ...
  ...
FROM wp_post_meta
GROUP BY post_id

The CASE statements determine which parameter you are pulling and assign it to a column. They are wrapped in MAX() aggregates simply to eliminate the NULLs which result when the keys don’t match, collapsing it down to a single row with columns for each attribute rather than multiple rows with mostly NULL values.

Failing this (if your set of attributes is varies unexpectedly), you would need to iterate in code. That would be messy though.

In PHP:

Using PHP, if you have an array of the meta post keys you want to retrieve, you can loop over all rows and if the meta_key is one you want, store the meta_value onto an array:

// Assumes your WP query results are already stored into the array $your_db_rows

// Will hold your final processed results
$output = array();
// If you want only a specific set of meta_key names rather than all meta_key names
$keys_you_want = array('_billing_first_name','_billing_last_name','_some_other_attribute');

// Loops over the result set
foreach ($your_db_rows_array as $row) {
  // If the current row holds one of the meta_key you are looking for
  if (in_array($row['meta_key'], $keys_you_want)) {
    // Put it onto the output array using the meta_key as the array key
    $output[$row['meta_key'] = $row['meta_value'];
  }
  // Otherwise do nothing...
}
var_dump($output);

To get all meta_key, just leave out the in_array() test and the $keys_you_want array. That will store every meta_key encountered onto $output.

// Loops over the result set for all values of meta_key, not a specific set
foreach ($your_db_rows_array as $row) {
  // Put it onto the output array using the meta_key as the array key
  $output[$row['meta_key'] = $row['meta_value'];
}
var_dump($output);