What is LocalDB and How to use it?

By | August 26, 2017

LocalDB is a new version of SQL Express. LocalDB is created specifically for developers. It is very easy to install and requires no management, yet it offers the same T-SQL language, programming surface and client-side providers as the regular SQL Server Express. In effect the developers that target SQL Server no longer have to install and manage a full instance of SQL Server Express on their laptops and other development machines. Moreover, if the simplicity (and limitations) of LocalDB fit the needs of the target application environment, developers can continue using it in production, as LocalDB makes a pretty good embedded database too.

LocalDB has the following key properties:

  1. LocalDB uses the same sqlservr.exe as the regular SQL Express and other editions of SQL Server. The application is using the same client-side providers (ADO.NET, ODBC, PDO and others) to connect to it and operates on data using the same T-SQL language as provided by SQL Express.
  2. LocalDB is installed once on a machine (per major SQL Server version). Multiple applications can start multiple LocalDB processes, but they are all started from the same sqlservr.exe executable file from the same disk location.
  3. LocalDB doesn’t create any database services; LocalDB processes are started and stopped automatically when needed. The application is just connecting to “Data Source=(localdb)\v11.0” and LocalDB process is started as a child process of the application. A few minutes after the last connection to this process is closed the process shuts down.
  4. LocalDB connections support AttachDbFileName property, which allows developers to specify a database file location. LocalDB will attach the specified database file and the connection will be made to it.

LocalDB Instances

As said before, at the heart of LocalDB is the same sqlservr.exe as in the regular SQL Express and other editions of SQL Server. In case of LocalDB, it is installed into one central location together with all necessary DLLs. By default it is located at “C:\Program Files\Microsoft SQL Server\110\LocalDB\Binn”.

When an application uses any of the client-side providers (like ADO.NET, ODBC or PDO) to connect to “Data Source=(localdb)\v11.0”, the provider will first check if LocalDB instance for the current user is started. If it’s already started the application will connect to it. Otherwise the LocalDB instance for the current user will be started and then the provider proceeds to connect to it. Note that each user (Windows login) may have their own LocalDB instance that is isolated from instances of other users.

Database as a File

LocalDB connection strings support AttachDbFileName property that allows attaching a database file during the connection process. This lets developers work directly with databases instead of the database server. Assuming a database file (*.MDF file with the corresponding *.LDF file) is stored at “C:\MyData\Database1.mdf” the developer can start working with it by simply using the following connection string: “Data Source=(localdb)\v11.0;Integrated Security=true;AttachDbFileName=C:\MyData\Database1.mdf”.

LocalDB and User Instances of SQL Express

Users familiar with today’s User Instances of SQL Server Express should feel right at home with LocalDB. In essence LocalDB offers the ability to create and start a “user instance” without the hassle of installing and maintaining the parent SQL Express instance. In that respect LocalDB could be seen as an upgrade of the User Instances feature of SQL Server Express.

LocalDB and SQL Express

LocalDB is not a replacement for SQL Server Express — it is an addition to SQL Server Express lineup. While LocalDB is meant for developers, the regular SQL Server Express will continue to exist as a free SQL Server edition, fully compatible with and easily upgradeable to higher SQL Server editions.

LocalDB and SQL Server Compact?

Small and simple database, lightweight installation, connecting to a database file — this will sound familiar to any developer using SQL Server Compact. The similarities are not accidental, as our goal for LocalDB was to be as easy to use as SQL Server Compact (while being as powerful and compatible with full SQL Server as SQL Express).

There are significant differences between LocalDB and SQL Server Compact:

  1. Execution mode: SQL Server Compact is an in-proc DLL, while LocalDB runs as a separate process.
  2. Disk usage: all SQL Server Compact binaries amount to some 4MBs, while LocalDB installation takes 140MBs.
  3. Features: SQL Server Compact offers core RDBMS functionality like querying, while LocalDB provides a much richer set of features, including Stored Procedures, Geometry and Geography data types, etc.


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