MariaDB 10.3

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create table wp_posts (
  ID integer primary key auto_increment,
  post_title varchar(30),
  post_type varchar(30)
);
create table wp_postmeta (
  ID integer primary key auto_increment,
  post_id integer,
  meta_key varchar(30) not null default '_regular_price',
  meta_value integer not null
);
insert into wp_posts (post_title, post_type) values
('Apple Pie','Product'),
('French Toast','Product'),
('Shepards Pie','Product'),
('Jam Pie','Product'),
('Jam Pie','Product'),
('Plate','Not a Product'),
('Bucket','Not a Product'),
('Chequebook','Not a Product'),
('French Toast','Product'),
('French Toast','Product'),
('Banana','Product'),
('Banana','Product'),
('Banana','Product');
insert into wp_postmeta (post_id, meta_value) values
(1,10),
(2,5),
(3,9),
(4,8),
(5,11),
(6,12),
(7,10),
(8,6),
(9,1),
(10,1),
(11,7),
(12,2),
(13,2);
-- Deleting all duplicate products in wp_posts table

DELETE FROM
wp_posts WHERE ID IN ( SELECT ID FROM
(
select ID,post_title,post_type,meta_value from 
(SELECT wp_postmeta.post_id,post_title,post_type ,meta_value,
row_number()over(partition by post_title order by wp_postmeta.meta_value) rn                           
FROM   wp_postmeta 
JOIN wp_posts ON wp_postmeta.post_id = wp_posts.id 
WHERE  wp_posts.post_type = 'Product' 
  AND wp_postmeta.meta_key = '_regular_price' 

) t where t.rn <> 1
) AS aliasx
);

-- Deleting all corresponding wp_postmeta.post_ids that don't have a match in wp_posts.id after the duplicate deletion above

Unknown column 'ID' in 'field list'