How to get the records of the first table that have no links in the records of the second table?

Question

PostgreSQL

There are two tables - posts and covers.
The covers has a "post_id" field.
How to get posts that don't have covers?
Tried to do something using JOIN, but didn't work...

Answer 1

SELECT `p`.`id`
  FROM `posts` AS `p`
  LEFT JOIN `covers` AS `c` ON `c`.`post_id` = `p`.`id`
  WHERE `c`.`post_id` IS NULL