Wordpress Multiple DB Rows Into Columns - mysql

Question

I want to retrieve the data of multiple product meta values for the same product but instead of displaying it in multiple rows I want the meta values as their own columns.
I start with:
SELECT a.post_title, b.meta_key, b.meta_value
FROM wp_posts a
INNER JOIN wp_postmeta b
ON a.ID = b.post_id
WHERE a.post_type = 'product'
AND b.meta_key = '_custom_animal_id'
OR b.meta_key = '_custom_breed';
This returns a table:
Name
meta_key
meta_value
Cow 1
_custom_animal_id
FR4380
Cow 1
_custom_breed
HO
Cow 2
_custom_animal_id
FR0001
Cow 2
_custom_breed
HO
Cow 3
_custom_animal_id
FR9999
Cow 3
_custom_breed
ZZ
What I want to display is:
Name
Animal ID
Breed
Cow 1
FR4380
HO
Cow 2
FR0001
HO
Cow 3
FR9999
ZZ
I know I will need to group by post_id (as a the title may not be unique) but returning the rows to columns I have searched a lot and not finding the answer to do it.

Answer 1

You can try to use the condition aggregate function.
MAX with CASE WHEN to make the pivot
SELECT a.post_title 'Name',
MAX(CASE WHEN b.meta_key = '_custom_animal_id' THEN b.meta_value END) 'Animal ID' ,
MAX(CASE WHEN b.meta_key = '_custom_breed' THEN b.meta_value END) 'Breed'
FROM wp_posts a
INNER JOIN wp_postmeta b
ON a.ID = b.post_id
WHERE a.post_type = 'product'
AND b.meta_key = '_custom_animal_id'
OR b.meta_key = '_custom_breed'
GROUP BY a.post_title
Results:
| Name | Animal ID | Breed |
|-------|-----------|-------|
| Cow 1 | FR4380 | HO |
| Cow 2 | FR0001 | HO |
| Cow 3 | FR9999 | ZZ |

Answer 2

Need to make use of a subquery here to get what we need. Make sure you have an appropriate index on wp_postmeta.meta_key if you haven't already.
SELECT a.post_title, animalid.meta_key, breed.meta_key
FROM wp_posts a
INNER JOIN (SELECT post_id, meta_key
FROM wp_postmeta
WHERE meta_key = '_custom_animal_id') animalid ON a.ID = animalid.post_id
INNER JOIN (SELECT post_id, meta_key
FROM wp_postmeta
WHERE meta_key = '_custom_breed') breed ON a.ID = breed.post_id
WHERE a.post_type = 'product';