SQL update row based on another row - mysql

Question

I have a wordpress database table called "wp_postmeta"
It looks like this (simplified)
Here is what I want to do in english, hopefully someone can help me translate this to an actual SQL statement.
if meta_key(address) LIKE "%Portland%", update meta_value(post_city_id) to be 7,17" where the post_id's are the same.
So in the end it would look like:
I tried this, but no rows selected when executed.
UPDATE wp_postmeta
SET wp_postmeta_bak.meta_value = "7,17"
WHERE wp_postmeta.meta_key = "post_city_id"
AND
wp_postmeta.meta_key = "address" AND wp_postmeta.meta_value LIKE "%Portland"
I read in another questions here about using temporary table, but thats above my pay grade.

Answer 1

Ahhh, the mysterious and wonderful wp_postmeta key/value store sows more mystery and wonder. You need a self-join to correlate the postmeta rows that relate to the same post_id values as each other.
You need to update the right side of a self-joined table.
UPDATE wp_postmeta a
JOIN wp_postmeta b ON a.post_id = b.post_id
AND b.meta_key = 'address'
AND b.meta_value LIKE '%Portland%'
SET a.meta_value = '7,17'
WHERE a.meta_key = 'post_city_id'
The JOIN will yield an empty resultset unless all three of the ON criteria match. Once it yields a nonempty result set, it will update the correct rows.
Before you do this update, you can test that it's choosing the right rows with this query.
SELECT a.meta_id, a.post_id, a.meta_key, a.meta_value,
b.meta_value AS address
FROM wp_postmeta a
JOIN wp_postmeta b ON a.post_id = b.post_id
AND b.meta_key = 'address'
AND b.meta_value LIKE '%Portland%'
WHERE a.meta_key = 'post_city_id'
The rows in post_meta that will be updated have the meta_id values shown in this result set.

Answer 2

You're not getting any results because you're telling the code two different exclusive things:
1) where meta_key = "post_city_id" AND
2) where same column = "address".
From what I can see, it's either one or the other. You can't have both. It's probably a typo.
WHERE wp_postmeta.meta_key = "post_city_id"
AND
wp_postmeta.meta_key = "address"
AND wp_postmeta.meta_value LIKE "%Portland"