At its core, Drupal is a tool for creating, maintaining, and displaying information stored in a database. Drupal database management is a crucial part of the entire system, as all aspects of a site are stored in the database.
It's pretty important, then, that the parts of Drupal that touch the database be pretty solid and efficient.
Prior to version 7 of Drupal, the system was pretty much locked into a single database product—MySQL. There were some successful implementations of Postgres/SQL, but virtually all development was done against MySQL and the vast majority of current implementations use MySQL.
In many ways, using Drupal with PHP is similar to the way we created our classic ASP programs. Either we'd write our ...