Choose SQL for related data, joins and transactions; choose NoSQL for key lookups, whole documents or very large write streams.
In October 2026, four of the five most popular databases on DB-Engines are relational, and PostgreSQL gained 45.6 points in a year.
The line has blurred: PostgreSQL, MySQL, SQL Server and Oracle all list document support.
In my test, a PostgreSQL jsonb column took new fields with no schema change, and a constant-default ALTER on 2 million rows took under half a second.
MongoDB does not use SQL; its edge is a flexible document model with built-in sharding.