MDF File

SQL Server Database File (.mdf)

What is a MDF file?

An MDF file is a Microsoft SQL Server database data file. It’s typically the primary data file for a database and contains tables, indexes, stored procedures, and other database objects and data pages.

Common uses

Storing SQL Server database data (primary data file)
Attaching/restoring databases in SQL Server
Moving databases between servers (with LDF/other files)
Development and testing database snapshots
Database recovery and forensics (advanced use)

How to open a MDF file

Windows: SQL Server Management Studio (SSMS) + SQL Server to attach/open
Developers: Use LocalDB/SQL Server Express for local testing
Tip: MDF usually pairs with an .ldf log file—keep them together when possible

Common problems

Can’t attach because SQL Server version is older/newer
Missing or mismatched LDF (transaction log) file
Permissions: SQL Server service account can’t access the file path
Corruption after crash or incomplete copy
Database already in use/locked when attaching

History

MDF has long been used as SQL Server’s main database data file format. Over time, SQL Server added features like multiple data files (NDF), improved recovery, and compatibility levels, but MDF remains the core container for database pages and objects.