However, there are several "near-portable" solutions and lightweight alternatives that can achieve the same goal. This guide covers how to get as close as possible to a portable SQL Server experience.
If you are looking for an official version that you can simply run from a USB drive without installation, the short answer is: it doesn't exist . Microsoft designs SQL Server as a service-based engine that requires deep integration with the Windows Registry and system services to function. ms sql server express portable
It runs in user mode rather than as a system service. It only starts when an application connects to it and shuts down when not in use. ms sql server express portable