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SqlConnection.Open Method

Opens a database connection with the property settings specified by the ConnectionString.

Namespace:  System.Data.SqlClient
Assembly:  System.Data (in System.Data.dll)

Public Overrides Sub Open




Cannot open a connection without specifying a data source or server.


The connection is already open.


A connection-level error occurred while opening the connection. If the Number property contains the value 18487 or 18488, this indicates that the specified password has expired or must be reset. See the ChangePassword method for more information.

The SqlConnection draws an open connection from the connection pool if one is available. Otherwise, it establishes a new connection to an instance of SQL Server.


If the SqlConnection goes out of scope, it is not closed. Therefore, you must explicitly close the connection by calling Close.


If you specify a port number other than 1433 when you are trying to connect to an instance of SQL Server and using a protocol other than TCP/IP, the Open method fails. To specify a port number other than 1433, include "server=machinename,port number" in the connection string, and use the TCP/IP protocol.


The .NET Framework Data Provider for SQL Server requires the Security permission with "Allows calls to unmanaged assemblies" enabled (SecurityPermission with SecurityPermissionFlag set to UnmanagedCode) to open a SqlConnection with SQL Debugging enabled.

The following example creates a SqlConnection, opens it, and displays some of its properties. The connection is automatically closed at the end of the using block.

Private Sub OpenSqlConnection(ByVal connectionString As String)
    Using connection As New SqlConnection(connectionString)
        Console.WriteLine("ServerVersion: {0}", connection.ServerVersion)
        Console.WriteLine("State: {0}", connection.State)
    End Using
End Sub

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.