Open Method

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 override void Open()

Exception Condition

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 <> tag in the app.config file has invalid or unknown elements.


There are two entries with the same name in the <localdbinstances> section.

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.

.NET Framework
Available since 1.1
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