SQL Multiple values from same column with inner join - mysql

Question

I am looking to join data from one table to another. The problem I have is in table two, the data I need is in the same column.
This is using wordpress/woocommerce DB so as you may be aware a lot of the user data is stored in the user meta table and you extract it by selecting the meta value where meta key = something
Rough data structure for user meta table
id | user_id | meta_key | meta_value
Now I select from table 1, inner join to table 2 and use the IN operator to select the meta values I want based on meta_key
select wp_xxxxxx_users.ID, wp_xxxxxx_users.user_email, wp_xxxxxxxxx.meta_value
from wp_xxxxxx_users
INNER JOIN wp_xxxxxx_usermeta on wp_xxxxxx_users.ID=wp_xxxxxx_usermeta.user_id
WHERE wp_xxxxxx_usermeta.meta_key IN ('last_name', 'first_name')
Now this returns all the data fine but in this format
id | user_email | meta_value
So what's wrong? Well I would like the meta_value columns to appear on the same row rather than multiple rows
I want the output to do the following
id | user_email | metavalue-first_name | metavalue-last_name
As it's currently outputting like so
1 | test#test.com | first name
1 | test#test.com | lastname name
2 | test1#test.com | first name
2 | test1#test.com | lastname name
I have a looked around relevant threads and seen people accomplishing this by Group By but I couldn't get it to work
Version is MySQL 5.7.27

Answer 1

You can do it if you group by ID, user_email and use conditional aggregation:
select
u.ID, u.user_email,
max(case m.meta_key when 'first_name' then m.meta_value end) first_name,
max(case m.meta_key when 'last_name' then m.meta_value end) last_name
from wp_xxxxxx_users u inner join wp_xxxxxx_usermeta m
on u.ID = m.user_id
where m.meta_key IN ('last_name', 'first_name')
group by u.ID, u.user_email

Answer 2

You didn't give any data.
So this tables
CREATE TABLE wp_xxxxxx_users (
ID int , user_email varchar(20));
INSERT INTO wp_xxxxxx_users (id,user_email) VALUES
(1,'test#mail.de'),
(2,'test1#mai.de'),
(3,'test2#mail.de');
CREATE TABLE wp_xxxxxx_usermeta
(`ID` int, `user_id` int, `meta_key` varchar(14), `meta_value` varchar(12))
;
INSERT INTO wp_xxxxxx_usermeta
(`ID`, `user_id`, `meta_key`, `meta_value`)
VALUES
(1, 1, 'last_name' , 'Dallas' ),
(2, 1, 'first_name' , 'Kermit' ),
(3, 2, 'last_name' , 'Huston' ),
(4, 2, 'first_name' , 'Piggy' ),
(5, 3, 'last_name' , 'Oklahoma' ),
(6, 3, 'first_name' , 'Beep' )
;
This Select statement
SELECT
wpu.ID
,wpu.user_email
, wpm.last_name
,wpm2.first_name
FROM wp_xxxxxx_users wpu
INNER JOIN
(SELECT meta_value as last_name, user_id FROM
wp_xxxxxx_usermeta Where meta_key = 'last_name') wpm
ON wpu.ID=wpm.user_id
INNER JOIN (SELECT meta_value as first_name, user_id from
wp_xxxxxx_usermeta WHERE meta_key = 'first_name') wpm2
ON wpu.ID=wpm2.user_id
;
or you can use
Select wpu.ID
,MAX(wpu.user_email),
MAX(CASE WHEN wpm.meta_key = 'last_name' THEN wpm.meta_value END) last_name,
MAX(CASE WHEN wpm.meta_key = 'first_name' THEN wpm.meta_value END) first_name
From wp_xxxxxx_users wpu inner join wp_xxxxxx_usermeta wpm
ON wpu.ID=wpm.user_id
WHERE wpm.meta_key in ('last_name','first_name')
GROUP by wpu.ID;
gives you following result
ID user_email last_name first_name
1 test#mail.de Dallas Kermit
2 test1#mai.de Huston Piggy
3 test2#mail.de Oklahoma Beep
You find here an example