Help understanding ER diagram Data Science/Business Analytics for Small Business Applications › Forums › SQL › Help understanding ER diagram Tagged: ER diagram, infinity symbol in ER diagram, primary key in SQL This topic is empty. Viewing 1 post (of 1 total) Author Posts April 16, 2022 at 5:32 am #118 AdminKeymaster https://www.coursera.org/learn/sql-for-data-science An explanation of why few tables are kept black as well how to make sense of primary key and infinity symbol appreciated. Reply It appears that some entities are blacked out because they really do not matter for the question being asked. The primary key symbol identifies the column(s) that make up the primary key. The infinity symbol identifies one-to-many relationships. Author Posts Viewing 1 post (of 1 total) You must be logged in to reply to this topic. Log In Username: Password: Keep me signed in Log In