WordPress SQL query the user’s first & last name for product X?

I am creating an SQL query where I want to display the full names and emails of customers who have purchased a downloadable product from a woocommerce shop. I am looking for something like this:

user_id    first_name    last_name    user_email    order
---------------------------------------------------------
1          Peter         Jones        a12@gmail     Doc_1

In the table above, Doc_1 stands for the name of the product, in this case the customer with user_id = 1 can download Doc_1. For wordpress users, you know that the table wp_usermeta contains all the user’s information, and looks like this:

umeta_id    user_id    meta_key    meta_value
---------------------------------------------
1           1          nickname    petjon123
2           1          first_name  Peter
3           1          last_name   Jones
...         ...        ...         ...

This list goes down containing more meta_value[s] including email, etc. Everything would have been much more easier if the meta_key[s] would be table headers showing first_name and last_name beside each other instead of on top one another. I have come this far where my query shows the first_name, but I am having trouble getting the last_name. My SQL query looks like this:

SELECT
  wp_usermeta.user_id,
  wp_usermeta.meta_value AS 'first_name',
  Wp_woocommerce_downloadable_product_permissions_1.user_email AS 'email',
  Wp_woocommerce_order_items_1.order_item_name AS 'order'
FROM Wp_woocommerce_order_items
     INNER JOIN Wp_woocommerce_downloadable_product_permissions
       ON Wp_woocommerce_order_items.order_id = Wp_woocommerce_downloadable_product_permissions.order_id,
     (Wp_woocommerce_order_items AS Wp_woocommerce_order_items_1
     INNER JOIN Wp_woocommerce_downloadable_product_permissions AS Wp_woocommerce_downloadable_product_permissions_1
       ON Wp_woocommerce_order_items_1.order_id = Wp_woocommerce_downloadable_product_permissions_1.order_id)
     INNER JOIN wp_usermeta
       ON Wp_woocommerce_downloadable_product_permissions_1.user_id = wp_usermeta.user_id
GROUP BY wp_usermeta.user_id,
         wp_usermeta.meta_value,
         Wp_woocommerce_downloadable_product_permissions_1.user_email,
         Wp_woocommerce_order_items_1.order_item_name,
         Wp_woocommerce_order_items_1.order_item_type,
         wp_usermeta.meta_key
HAVING (((Wp_woocommerce_order_items_1.order_item_type) = 'line_item')
AND ((wp_usermeta.meta_key) = 'first_name'));

Giving me this result:

user_id    first_name    user_email    order
--------------------------------------------
1          Peter         a12@gmail     Doc_1

I checked these values manually, and they are correct, however, I must say that if I do not GROUP the results, I get 1000 times more results, so GROUPING the data simplifies the results by basically removing the duplicates which obviously is excessive. I am doubting that this query is efficient given that the execution time until the results appear is +/-20368.14 ms and hereby am very open to any suggestions of improving this code. Having this said, I thought that I had to do another query to get the last_name making this a NESTED QUERY. If I open the tables in MS Access, create lets say Query1 which is the query above, and join Query1 with the table I get the results that I want. The SQL code for this is as follows:

SELECT
  Query1.user_id,
  Query1.first_name,
  wp_usermeta.meta_value AS 'last_name',
  Query1.user_email,
  Query1.order_item_name
FROM wp_usermeta
INNER JOIN Query1
  ON wp_usermeta.user_id = Query1.user_id
WHERE (((wp_usermeta.meta_value) <> '')
AND ((wp_usermeta.meta_key) = 'last_name'));

I tried substituting Query1 for this second query using parenthesis by enclosing the code from Query1, and this did not work. I get this error:

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ‘.user_id, (SELECT wp_usermeta.user_id, wp_usermeta.meta_value AS ‘first’ at line 22

Does anybody know how to do this? Thanks!!

UPDATE

According to the answer provided by @Hogan I came up with this:

SELECT
  first.user_id,
  first.meta_value AS 'first_name',
  last.meta_value AS 'last_name',
  Wp_woocommerce_downloadable_product_permissions_1.user_email,
  Wp_woocommerce_order_items_1.order_item_name
FROM Wp_woocommerce_order_items
     INNER JOIN Wp_woocommerce_downloadable_product_permissions
       ON Wp_woocommerce_order_items.order_id = Wp_woocommerce_downloadable_product_permissions.order_id,
     wp_usermeta AS last
     INNER JOIN ((Wp_woocommerce_order_items AS Wp_woocommerce_order_items_1
     INNER JOIN Wp_woocommerce_downloadable_product_permissions AS Wp_woocommerce_downloadable_product_permissions_1
       ON Wp_woocommerce_order_items_1.order_id = Wp_woocommerce_downloadable_product_permissions_1.order_id)
     INNER JOIN wp_usermeta AS first
       ON Wp_woocommerce_downloadable_product_permissions_1.user_id = first.user_id)
       ON last.user_id = Wp_woocommerce_downloadable_product_permissions_1.user_id
GROUP BY first.user_id,
         first.meta_value,
         last.meta_value,
         Wp_woocommerce_downloadable_product_permissions_1.user_email,
         Wp_woocommerce_order_items_1.order_item_name,
         Wp_woocommerce_order_items_1.order_item_type,
         first.meta_key,
         last.meta_key
HAVING (((Wp_woocommerce_order_items_1.order_item_type) = 'line_item')
AND ((first.meta_key) = 'first_name')
AND ((last.meta_key) = 'last_name'));

Which works perfectly fine in MS Access but in SQL it does not. I am getting this error:

Unknown column ‘first.meta_key’ in ‘having clause’

Why?

I also have to mention, that when I add the meta_key[s] to the SELECT like this:

SELECT
  first.user_id,
  first.meta_value AS 'first_name',
  last.meta_value AS 'last_name',
  Wp_woocommerce_downloadable_product_permissions_1.user_email,
  Wp_woocommerce_order_items_1.order_item_name,
  first.meta_key,
  last.meta_key

I at least get no error, the query is running but it goes on and on increasing my CPU usage drastically given that I am working on a localhost.

SOLUTION

SELECT DISTINCT did the trick. No GROUPING. The query results appear in 127.76 ms. This is my query:

SELECT DISTINCT
  first.user_id AS 'id',
  first.meta_value AS 'first_name',
  last.meta_value AS 'last_name',
  Wp_woocommerce_downloadable_product_permissions_1.user_email AS 'email',
  Wp_woocommerce_order_items_1.order_item_name AS 'order'
FROM Wp_woocommerce_order_items
     INNER JOIN Wp_woocommerce_downloadable_product_permissions
       ON Wp_woocommerce_order_items.order_id = Wp_woocommerce_downloadable_product_permissions.order_id,
     ((Wp_woocommerce_order_items AS Wp_woocommerce_order_items_1
     INNER JOIN Wp_woocommerce_downloadable_product_permissions AS Wp_woocommerce_downloadable_product_permissions_1
       ON Wp_woocommerce_order_items_1.order_id = Wp_woocommerce_downloadable_product_permissions_1.order_id)
     INNER JOIN wp_usermeta AS first
       ON Wp_woocommerce_downloadable_product_permissions_1.user_id = first.user_id)
     INNER JOIN wp_usermeta AS last
       ON Wp_woocommerce_downloadable_product_permissions_1.user_id = last.user_id
WHERE (((first.meta_key) = 'first_name')
AND ((last.meta_key) = 'last_name')
AND ((Wp_woocommerce_order_items_1.order_item_type) = 'line_item'));

As @Hogan stated, simply add the table wp_usermeta again with another alias, and make an INNER JOIN.