Whenever I am teaching a database class it seems I always get the question of what is the most popular Relational Database Management Systems (RDBMS). I always refer to the DB-Engine Ranking monthly trend website. The problem is I keep forgetting where the website is located. So for myself and for my students I am putting a link here. So I have it as a quick resource. As you can see, Oracle, MySQL, and SQL Server lead the group by a wide margin. With 14 of the top 25, RDBMS still seems to be the ruler of databases.