Question

When I execute the following query:

DELETE FROM wp_postmeta 
    WHERE post_id 
        NOT IN (
            SELECT post_id 
            FROM wp_postmeta a 
            INNER JOIN wp_sl_posts b 
            ON a.post_id = b.id
            )

I get an error message:

You can't specify target table 'wp_postmeta' for update in FROM clause  

I sort of know why, but I really don’t know the syntax required here to perform the operation. I’ve tried a few different alternatives based on answers here and elsewhere, but not luck.

Answer 1

try

DELETE wp_postmeta 
FROM wp_postmeta 
left outer JOIN wp_sl_posts b ON a.post_id = b.id
WHERE b.post_id is null