Wordpress SQL: get post category and tags

Question

I want to query Wordpress data stored in a MySQL database, in order to get a result with columns:

1. post_id
2. category
3. comma-separated tags

Expected output:

+---------------+----------+----------------+
| post_id       | category | tags           |
|---------------+----------+----------------+
| 213           | news     | tag1,tag2,tag3 |
+---------------+----------+----------------+

Here's what I have tried:

SELECT
    p.id,
    c.name,
    GROUP_CONCAT(t.`name`)
FROM wp_posts p
JOIN wp_term_relationships cr 
    on (p.`id`=cr.`object_id`)
JOIN wp_term_taxonomy ct 
    on (ct.`term_taxonomy_id`=cr.`term_taxonomy_id` and ct.`taxonomy`='category')
JOIN wp_terms c 
    on (ct.`term_id`=c.`term_id`)
JOIN wp_term_relationships tr 
    on (p.`id`=tr.`object_id`)
JOIN wp_term_taxonomy tt 
    on (tt.`term_taxonomy_id`=tr.`term_taxonomy_id` 
   and tt.`taxonomy`='post_tag')
JOIN wp_terms t 
    on (tt.`term_id`=t.`term_id`)

As a result, I get the columns I want, with the expected content, but I only get one row.

What am I doing wrong?

Answer 1

As noted in the comments, I was including an aggregate function, but no "group by" clause.

Now this seems to work (just added the GROUP BY line):

SELECT
    p.id,
    p.post_name,
    c.name,
    GROUP_CONCAT(t.`name`)
FROM wp_posts p
JOIN wp_term_relationships cr
    on (p.`id`=cr.`object_id`)
JOIN wp_term_taxonomy ct
    on (ct.`term_taxonomy_id`=cr.`term_taxonomy_id`
    and ct.`taxonomy`='category')
JOIN wp_terms c on
    (ct.`term_id`=c.`term_id`)
JOIN wp_term_relationships tr
    on (p.`id`=tr.`object_id`)
JOIN wp_term_taxonomy tt
    on (tt.`term_taxonomy_id`=tr.`term_taxonomy_id`
    and tt.`taxonomy`='post_tag')
JOIN wp_terms t
    on (tt.`term_id`=t.`term_id`)
GROUP BY p.id


+---------------+----------+----------------+
| post_id       | category | tags           |
|---------------+----------+----------------+
| 213           | news     | tag1,tag2,tag3 |
+---------------+----------+----------------+
| 216           | whatever | tag2,tag3      |
+---------------+----------+----------------+

Thank you Strawberry!

Answer 2

This is based off of Pierre's code, expanded to concatenate multiple categories, as well as include posts with no categories or tags.

SELECT
    p.id,
    p.post_name,
    GROUP_CONCAT(DISTINCT c.`name`) as categories,
    GROUP_CONCAT(DISTINCT t.`name`) as tags
FROM wp_posts p
LEFT JOIN wp_term_relationships cr
    on (p.`id`=cr.`object_id`)
LEFT JOIN wp_term_taxonomy ct
    on (ct.`term_taxonomy_id`=cr.`term_taxonomy_id`
    and ct.`taxonomy`='category')
LEFT JOIN wp_terms c on
    (ct.`term_id`=c.`term_id`)
LEFT JOIN wp_term_relationships tr
    on (p.`id`=tr.`object_id`)
LEFT JOIN wp_term_taxonomy tt
    on (tt.`term_taxonomy_id`=tr.`term_taxonomy_id`
    and tt.`taxonomy`='post_tag')
LEFT JOIN wp_terms t
    on (tt.`term_id`=t.`term_id`)
GROUP BY p.id