Group data from two tables, multiple columns and rows, into one row - mysql

Question

I'm trying to group key = value pairs that are each on its row, into one row groupped by ID.
table 1. wp_posts
keys: ID - post_title
table 2. wp_postmeta
keys: post_id, wpcf-owner, wpcf- tel, wpcf-mob, wpcf-email...
Using this query, I'm getting all info, but for each key I get separate row. What I need is an array where all is in one row groupped by wp_posts.ID
SELECT wp_posts.ID, wp_posts.post_title, wp_postmeta.post_id, wp_postmeta.meta_key, wp_postmeta.meta_value
FROM wp_posts
JOIN wp_postmeta
ON wp_posts.ID = wp_postmeta.post_id
WHERE wp_posts.post_type = 'accommodation' AND wp_postmeta.meta_key LIKE 'wpcf%'
ORDER BY hic13_posts.post_title
Result is:
ID | post_title | key value
------------------------------
1 | TITLE | wpcf-owner
1 | TITLE | wpcf-tel
1 | TITLE | wpcf-mob
1 | TITLE | wpcf-email
2 | TITLE | wpcf-owner
2 | TITLE | wpcf-tel
2 | TITLE | wpcf-mob
2 | TITLE | wpcf-email
...
What I need is:
ID | post_title | key value | key value | key value | key value
-----------------------------------------------------------------
1 | TITLE | wpcf-owner | wpcf-tel | wpcf-mob | wpcf-email
2 | TITLE | wpcf-owner | wpcf-tel | wpcf-mob | wpcf-email
If I add command to group by ID, then I get only one key from second table...
SELECT wp_posts.ID, wp_posts.post_title, wp_postmeta.post_id, wp_postmeta.meta_key, wp_postmeta.meta_value
FROM wp_posts
JOIN wp_postmeta
ON wp_posts.ID = wp_postmeta.post_id
WHERE wp_posts.post_type = 'accommodation' AND wp_postmeta.meta_key LIKE 'wpcf%'
GROUP BY hic13_posts.ID
ORDER BY hic13_posts.post_title
I get only this
ID | post_title | key value
------------------------------
1 | TITLE | wpcf-owner
2 | TITLE | wpcf-tel
Hope all this makes sense :-)
Thank you!

Answer 1

This type of transformation is a pivot but MySQL does not have a pivot function so you will need to use an aggregate function with a CASE expression.:
SELECT p.ID,
p.post_title,
m.post_id,
max(case when m.meta_key = 'wpcf-owner' then m.meta_value end) as owner,
max(case when m.meta_key = 'wpcf-tel' then m.meta_value end) as tel,
max(case when m.meta_key = 'wpcf-mob' then m.meta_value end) as mob,
max(case when m.meta_key = 'wpcf-email' then m.meta_value end) as email
FROM wp_posts p
JOIN wp_postmeta m
ON p.ID = m.post_id
WHERE p.post_type = 'accommodation' AND m.meta_key LIKE 'wpcf%'
GROUP BY p.ID, p.post_title, m.post_id
ORDER BY p.post_title
Edit, if you have an unknown number of meta_key items to transform, then you can use a prepared statement to generate dynamic sql:
SET #sql = NULL;
SELECT
GROUP_CONCAT(DISTINCT
CONCAT(
'max(CASE WHEN m.meta_key = ''',
meta_key,
''' THEN m.meta_value else null END) AS `',
meta_key, '`'
)
) INTO #sql
FROM wp_postmeta;
SET #sql
= CONCAT('SELECT p.ID,
p.post_title,
m.post_id, ', #sql, '
FROM wp_posts p
JOIN wp_postmeta m
ON p.ID = m.post_id
WHERE p.post_type = ''accommodation''
AND m.meta_key LIKE ''wpcf%''
GROUP BY p.ID, p.post_title, m.post_id
ORDER BY p.post_title');
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;