SQL query to find posts without tags

Question

MySQL

Greetings! I ask for help in compiling a SQL query.
Structure:

post (id | title | content)
tag (id | title)
post_tag (id | post_id | tag_id)

We need the id of those posts to which no tag is attached.

Answer 1

select id from post where post.id not in (select post_id from post_tag)