How to generate the E-R Diagram of Wordpress using mySQL Workbench
The EER diagram is correct. There should be no relationships because WordPress does not have any constraints. The EER diagram shown in the codex is only for reference (it's a dummy EER diagram). You must rely on other logical operations to make sure you have no orphaned data.

Source: https://codex.wordpress.org/Database_Description


  Please note that within the standard installation of WordPress no
  integrity between the tables is enforced e.g. between posts and
  comments. If you are creating a plugin or extension that manipulates
  the WordPress database, your code should do the housekeeping so that
  no orphan records remain in the tables e.g. by removing records in
  other tables with a set of SQL commands when foreign keys are deleted
  (Don't forget to remind users to backup before such operations).