At Stack Overflow, our environment has multiple implementations of a largely – but not 100% – identical schema. (By “schema,” I mostly mean the set of tables within a database.) I sometimes need to retrieve or update data across a large number of sites. Let’s say, pulling or removing information from the
Userstable, and related tables, across all of our databases.
Most of the time, we think of “schema drift” as “different from a Platonic ideal of our schema” and try to correct it. In this case, Aaron shows how we can still write queries while embracing schema drift as a basic fact.