如何在mysql for Wordpress数据库中将行值转换为列标题

Question

Using the following query I have fetched results from wp_posts and wp_postmeta table.

SELECT a., b. FROM wp_posts a, wp_postmeta b WHERE a.ID = b.post_id AND a.post_status = 'publish' AND a.post_type='wpsc-product'

From the above result, I want to filter the results to one more stage

As you know wp_postmeta structure is like

meta_id | post_id | meta_key | meta_value

I want to make all the meta_key values of the result to column names and its corresponding value as its value.

For eg if the table is like:

Meta_id-----------post_id-----------meta_key-----------meta_value

1-----------------31--------------mk1----------------mv1

2-----------------31--------------mk2----------------mv2

3-----------------31--------------mk3----------------mv3

The expected result is:

Meta_id-----------post_id-----------mk1--------mk2---------mk3

1-----------------31-----------------mv1---------mv2---------mv3

Is this possible??? I want this along with my join query.

The formatting of question is not correct. Please forgive for that.

Answer 1

You can use CASE if there are limited meta_keys

SELECT a.*,b.Meta_id, b.post_id,
CASE WHEN b.meta_key ='mk1' THEN b.meta_value END `mk1`,
CASE WHEN b.meta_key ='mk2' THEN b.meta_value END `mk2`,
CASE WHEN b.meta_key ='mk3' THEN b.meta_value END `mk3`
FROM wp_posts a
JOIN wp_postmeta b ON( a.ID = b.post_id )
WHERE a.post_status = 'publish' 
AND a.post_type='wpsc-product'
AND b.meta_key IN('mk1','mk2','mk3')

Edit for duplicates issue you can use JOINs

SELECT p.*,
a.Meta_id, 
a.post_id,
a.meta_value mk1, 
b.meta_value mk2,
c.meta_value mk3
FROM wp_posts p  
LEFT JOIN  wp_postmeta a ON(p.ID =a.post_id)
JOIN  wp_postmeta b USING(post_id) /* is equal to ON(b.post_id = a.post_id) */
JOIN  wp_postmeta c USING(post_id)
WHERE a.meta_key = 'mk1'
AND b.meta_key = 'mk2'
AND c.meta_key='mk3'

Fiddle Demo only for meta table