How to Change my Select SQL to Update SQL? - mysql

Question

I have managed to write the following SQL that gives me all records that have the same value in _price, _regular_price & _sale_price.
I need to update _sale_price on these records only to ' ' (nothing / empty)
Here is my working Select:
SELECT p.id, p.post_title, p1.meta_key, p1.meta_value, p2.meta_key, p2.meta_value, p3.meta_key, p3.meta_value
FROM sm_posts p
INNER JOIN sm_postmeta p1 ON p.id = p1.post_id
AND p1.meta_key = '_price'
INNER JOIN sm_postmeta p2 ON p.id = p2.post_id
AND p2.meta_key = '_regular_price'
INNER JOIN sm_postmeta p3 ON p.id = p3.post_id
AND p3.meta_key = '_sale_price'
WHERE p1.meta_value = p2.meta_value AND p1.meta_value = p3.meta_value
I need to create an Update from this but cant figure it out.
So far I have this but its not working:
UPDATE sm_postmeta2,
(
SELECT p.id, p.post_title, p1.meta_key, p1.meta_value, p2.meta_key, p2.meta_value, p3.meta_key, p3.meta_value
FROM sm_posts p
INNER JOIN sm_postmeta2 p1 ON p.id = p1.post_id
AND p1.meta_key = '_price'
INNER JOIN sm_postmeta2 p2 ON p.id = p2.post_id
AND p2.meta_key = '_regular_price'
INNER JOIN sm_postmeta2 p3 ON p.id = p3.post_id
AND p3.meta_key = '_sale_price'
WHERE p1.meta_value = p2.meta_value AND p1.meta_value = p3.meta_value
GROUP BY p1.ID
)
SET sm_postmeta2.meta_value = ''
WHERE sm_postmeta2.meta_value.id = p1.id
Please can someone help, i am new to SQL and it took me forever just to get the joins working. lol
Thank you for taking the time to help me.

Answer 1

Your error means that you must alias the subquery. However, you don't want to put the subquery in the UPDATE clause. If you do, MySQL either won't allow it, or it will update the temporary table resulting from the subquery, i.e. the changes wouldn't persist. Instead, you can INNER JOIN on the subquery to get the rows you want to update.
Since you're just using the subquery to determine the rows to update, you don't need to SELECT all the same values as before. Instead, you can just SELECT the primary key for the records you want to update.
Here's an example:
UPDATE sm_postmeta2 INNER JOIN
(
SELECT DISTINCT p3.meta_id
FROM sm_posts p
INNER JOIN sm_postmeta2 p1 ON p.id = p1.post_id
AND p1.meta_key = '_price'
INNER JOIN sm_postmeta2 p2 ON p.id = p2.post_id
AND p2.meta_key = '_regular_price'
INNER JOIN sm_postmeta2 p3 ON p.id = p3.post_id
AND p3.meta_key = '_sale_price'
WHERE p1.meta_value = p2.meta_value AND p1.meta_value = p3.meta_value
) p_tmp ON sm_postmeta2.meta_id = p_tmp.meta_id
SET sm_postmeta2.meta_value = ''