These database changes is for that case you havn't done modifications yet.
You don't want to loose data, but you need your db work fine.

alter table prefix_educourses add column start_agregate char(255);
alter table prefix_educourses add column stop_agregate char(255);
alter table prefix_posts add column hidden int(1) DEFAULT 0;
alter table prefix_comments add column hidden int(1) DEFAULT 0;

LATEST CHANGES IN DB
following tells to db that no duplication in relations tables anymore:
ALTER IGNORE TABLE prefix_course_rels_comments ADD PRIMARY KEY (course_guid, link);
ALTER IGNORE TABLE prefix_course_rels_posts ADD PRIMARY KEY (course_guid, link);


LATEST LATEST CHANGES
ALTER IGNORE TABLE prefix_comments ADD COLUMN post_author char(255);