I added posts from other CMS to my new word press site. For featured images I changed, wp_post
table as
post ID: 2300
Attachment in "wp_post":
ID:3400
post_type: attachment
post_mime_type: images/jpeg
post_parent: 2300
post_title: file name
post_name: fileName-in-WP-Content-upload
post_status:inherit
guid: site.com/upload/oldImages/fileName-in-WP-Content-upload.jpg
Making Featured image in "wp_postmeta"
post_id:2300
meta_key: _thmubnail_id
meta_value: 3400
Now I am not seeing featured image in post however I can see the image url with
echo wp_get_attachment_url( get_post_thumbnail_id(3400) );