我最终解决了这个问题，通过在post id列中添加大量数字，然后导出内容来防止id冲突。

我运行的查询是

; Update the post ids of all attachments. I choose 1000,000 since I already had more than 100,000 posts.
update wp_posts set id = id + 1000000 where post_type = \'attachment\';

; Update the postmeta fields of all attachments
update wp_postmeta set post_id = post_id + 1000000 where meta_key = \'_wp_attachment_metadata\';
update wp_postmeta set post_id = post_id + 1000000 where meta_key = \'_wp_attachment_image_alt\';
update wp_postmeta set post_id = post_id + 1000000 where meta_key = \'_wp_attached_file\';


; Update the featured image ids
update wp_postmeta set meta_value = meta_value + 1000000 where meta_key = \'_thumbnail_id\'

; You needs this if you are using featured images for terms. Change the meta key to whatever you are using.
update wp_termmeta set meta_value = meta_value + 1000000 where meta_key = \'featured_image_id\' and meta_value > 0;