把自定义字段修改成你的,执行SQL就行,记得务必先备份数据库
delete from wp_postmeta where meta_id in ( select * from ( select meta_id from wp_postmeta a where a.meta_key = '你的自定义字段' and meta_id not in ( select min(meta_id) from wp_postmeta b where b.post_id = a.post_id and b.meta_key = '你的自定义字段' ) ) as x );