Merging multiple rows into one row and multiple columns on mysql

Question

I am working in MYSQL and need to extract user data to be pulled into a view. I will be using the data in an email client, so I cannot do this in the app layer.

The

Answer 1

The previous answer and comments give the correct solution. Here is the working query (in schema for WP 3.1) for copy and paste...

SELECT distinct u.id, u.user_email,
   fn.meta_value AS first_name,
   ln.meta_value AS last_name
FROM wp_users AS u
LEFT JOIN wp_usermeta AS fn ON u.id = fn.user_id
   AND fn.meta_key = 'first_name'
LEFT JOIN wp_usermeta AS ln ON u.id = ln.user_id
   AND ln.meta_key = 'last_name'

Answer 2

Here is an another solution that doesn't need additional join operations, instead, we make use of group by statement along with case statement.

select um.user_id,
       max(case when um.meta_key ='first_name' then um.meta_data end) AS first_name,  
       max(case when um.meta_key ='last_name' then um.meta_data end) AS last_name  ,
       max(case when um.meta_key ='email' then um.meta_data end) AS email
from wp_usermeta um 
group by user_id;

Note the max function is just for making them into one row, you can use min as well.

Check SQL Fiddler Demo here

Answer 3

If these are the only columns you are concerned with, this will work for you:

SELECT um.user_id
   , fn.meta_data AS first_name
   , ln.meta_data AS last_name
   , e.meta_data AS email
FROM wp_userMeta AS um
LEFT JOIN wp_user_Meta AS fn ON um.user_id = fn.user_id
   AND fn.meta_key = 'first_name'
LEFT JOIN wp_user_Meta AS ln ON um.user_id = ln.user_id
   AND ln.meta_key = 'last_name'
LEFT JOIN wp_user_Meta AS e ON um.user_id = e.user_id
   AND e.meta_key = 'email'