If you are looking for an official MS SQL Server Express Portable 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.
If you absolutely must have a zero-install, portable SQL database that understands T-SQL, consider these alternatives: ms sql server express portable
Even in its most "portable" form (LocalDB), SQL Server Express enforces the following hardware caps: Limited to the lesser of 1 socket or 4 cores. Max 1 GB of RAM used by the buffer pool. If you are looking for an official MS
Simple Execution: It starts on demand when an application connects to it. Max 1 GB of RAM used by the buffer pool
You are a DBA needing to test queries on a locked-down machine without installing: