Joining tables to themselves and to eachother - php

Question

I've spent most of my day trying to figure this out so I guess it's time I ask the experts:
I'm trying to access my WordPress DB outside of WordPress, so I'm writing queries to get output from the somewhat complicated WordPress database.
There are several tables in the DB that use meta_values and meta_keys to store data about a post or user in multiple rows.
For Example here are four tables I need to pull from:
table: wp_postmeta
post_id | meta_key | meta_value
---------+-----------------+------------
2001 | _customer_user | 3
2001 |order_description| smith
2001 | _order_total | 300
table: wp_posts
ID | post_type | post_status
----+-----------+------------
2001| shop_order| publish
table: wp_term_relationships
object_id | term_taxonomy_id
----------+-----------------
2001 | 190
table: wp_usermeta
user_id | meta_key |meta_value
---------+-----------------+----------
3 | first_name | Andy
3 | last_name | Mccormick
I've got this query to work great to display the Order Number (post_id) Customer ID, Order Description, and Order total in a single row:
SELECT wp_posts.ID, wp_posts.post_title,ot.meta_value as total,od.meta_value as order_desc, cu.meta_value as customer
FROM wp_posts
LEFT JOIN wp_postmeta AS ot ON (wp_posts.ID = ot.post_id AND ot.meta_key='_order_total')
LEFT JOIN wp_postmeta AS od ON (wp_posts.ID = od.post_id AND od.meta_key='order_description')
LEFT JOIN wp_postmeta AS cu ON (wp_posts.ID =cu.post_id AND cu.meta_key='_customer_user')
LEFT JOIN wp_term_relationships ON wp_posts.ID = wp_term_relationships.object_id
WHERE wp_posts.post_type = 'shop_order'
AND wp_posts.post_status = 'publish'
AND wp_term_relationships.term_taxonomy_id = '190'
GROUP BY wp_posts.ID ORDER BY wp_posts.post_date DESC"
However in another area I want to list the customers by name and not just by ID so I'm trying to get their first and last name from the wp_usermeta table like this:
SELECT wp_posts.ID, cu.meta_value as customer, fn.meta_vale as fname, ln.meta_value as lname
FROM wp_posts
LEFT JOIN wp_postmeta AS cu ON (wp_posts.ID = cu.post_id AND cu.meta_key='_customer_user')
LEFT JOIN wp_usermeta AS fn ON (cu.meta_key = fn.user_id AND fn.meta_key='first_name')
LEFT JOIN wp_usermeta AS ln ON (cu.meta_key = ln.user_id AND ln.meta_key='last_name')
LEFT JOIN wp_term_relationships ON wp_posts.ID = wp_term_relationships.object_id
WHERE wp_posts.post_type = 'shop_order'
AND wp_posts.post_status = 'publish'
AND wp_term_relationships.term_taxonomy_id = '190'
GROUP BY wp_posts.ID ORDER BY wp_posts.post_date DESC;
I've also tried:
LEFT JOIN wp_usermeta AS fn ON ((cu.meta_key='_customer_user') = fn.user_id AND fn.meta_key='first_name') along with a host of other subqueries and such.
Obviously I'm above my pay-grade in SQL queries right now so any help would be great. thanks!

Answer 1

I'm not sure, but you might try this:
SELECT wp_posts.ID, cu.meta_value as customer, fn.meta_vale as fname, ln.meta_value as lname
FROM wp_posts
LEFT JOIN wp_postmeta AS cu ON (wp_posts.ID = cu.post_id AND cu.meta_key='_customer_user')
LEFT JOIN wp_usermeta AS fn ON (cu.meta_value = fn.user_id AND fn.meta_key='first_name') // Note meta_value instead of meta_key
LEFT JOIN wp_usermeta AS ln ON (cu.meta_value = ln.user_id AND ln.meta_key='last_name') // Note meta_value instead of meta_key
LEFT JOIN wp_term_relationships ON wp_posts.ID = wp_term_relationships.object_id
WHERE wp_posts.post_type = 'shop_order'
AND wp_posts.post_status = 'publish'
AND wp_term_relationships.term_taxonomy_id = '190'
GROUP BY wp_posts.ID ORDER BY wp_posts.post_date DESC;
From what I've figured out, cu.meta_value is 3 in your example as it's the user's id, while cu.meta_key (as in your query) is '_customer_id', so you rather want to match cu.meta_value than cu.meta_key. Couldn't check though, as I have no WP installation laying around.