Wordpress users and usermeta - joining multiple rows in one table to one row in another table

Question

I want to create a view from both the wp_users and wp_usermeta tables so that I can query rows in the view from an external application. Basic auth details are stored in wp_users (e.g. username, password, email, id) and other fields are stored in key/value pairs in the wp_usermeta table.

the wp_users table is structured like this:

id | login | password | email
-----------------------------
1  | bsmith| abc123   | [email protected]
2  | jjones| def456   | [email protected]

the wp_usermeta table is structured like this:

id | user_id | meta_key | meta_value
------------------------------------
1  | 1       | firstname| bob
2  | 1       | lastname | smith
3  | 1       | country  | denmark
4  | 2       | firstname| jan
5  | 2       | lastname | jones
6  | 2       | country  | germany

I want to end up with data like this as a MYSQL VIEW:

id | login | password | email    | firstname | lastname | country
-----------------------------------------------------------------
1  | bsmith| abc123   | [email protected]| bob       | smith    | denmark
2  | jjones| def456   | [email protected]| jan       | jones    | germany

I know I need to do at least an inner join between wp_users and wp_usermeta, however I also need to perform a sub query inside wp_usermeta to join those rows together.

The query I have for getting the user row is of course dead easy:

select u1.id, u1.login, u1.password, u1.email from wp_users u1

The query I have for getting the meta as a row this is:

select m1.user_id, m1.meta_value as firstname, m2.meta_value as lastname, m3.meta_value as country
from wp_usermeta m1
join wp_usermeta m2 on (m1.user_id = m2.user_id and m2.meta_key = 'last_name')
join wp_usermeta m3 on (m2.user_id = m3.user_id and m3.meta_key = 'country')
where m1.meta_key = 'first_name'

So how do I join these two queries together - u1's data and the row where u1.id = m1.userid?

Answer 1

As far as I know, you are doing it the right way and just need to put them all together:

SELECT
    u1.id,
    u1.login,
    u1.password,
    u1.email,
    m1.meta_value AS firstname,
    m2.meta_value AS lastname,
    m3.meta_value AS country
FROM wp_users u1
JOIN wp_usermeta m1 ON (m1.user_id = u1.id AND m1.meta_key = 'first_name')
JOIN wp_usermeta m2 ON (m2.user_id = u1.id AND m2.meta_key = 'last_name')
JOIN wp_usermeta m3 ON (m3.user_id = u1.id AND m3.meta_key = 'country')
WHERE
    -- CONDITIONS ON the user you want to select based any field

Answer 2

I found that Toote's solution works but is a performance hog on a MySQL database taking about 17 seconds to execute a "select * from users_with_meta_view".

I got this down to 0.0054 sec with a view structured like this instead:

CREATE OR REPLACE VIEW users_with_meta_view AS
SELECT
    u.id,
    u.user_login AS login,
    u.user_pass AS password,
    u.user_email AS email,
    (select meta_value from wp_usermeta where user_id = u.id and meta_key = 'first_name' limit 1) as first_name,
    (select meta_value from wp_usermeta where user_id = u.id and meta_key = 'last_name' limit 1) as last_name,
    (select meta_value from wp_usermeta where user_id = u.id and meta_key = 'country' limit 1) as country
FROM wp_users u