Question

I define Sql_Cmd And Other sql variable that need before
and Now write this code:

string strConnection2 = "Data Source=.\\sqlexpress;AttachDbFilename=master.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True";
SqlConnection sqlcon2 = new SqlConnection(strConnection2);
string sql = "select * ";
Sql_Cmd.CommandType = CommandType.Text;
Sql_Cmd.CommandText = sql;
Sql_Cmd.Connection = sqlcon2;
try
{
    sqlcon2.Open();
    Sql_Cmd.ExecuteNonQuery();
}
catch (SqlException Error_Exception)
{
    //FormError1 = new FormErrorInDataBase();
    //FormError1.Show();
}

When I want to open sqlcon2 I see this error:

An attempt to attach an auto-named database for file master.mdf failed. A database with the same name exists, or specified file cannot be opened, or it is located on UNC share.

Please help me – how can I open master database and then use select query for this database, and what is the connection string for master.mdf?

Can I write the directory of mater.mdf such as C:\Program Files\Microsoft SQL Server\MSSQL10.SQLEXPRESS\MSSQL\DATA\master.mdf or is it enough that I write AttachDbFilename=master.mdf?

Answer 1

Check your parameters again. The right syntax to add an .mdf-file is as follows. Attach a database file on connect to a local SQL Server Express instance:

Server=.\SQLExpress;AttachDbFilename=c:\asd\qwe\mydbfile.mdf;Database=dbname; Trusted_Connection=Yes;

Why is the Database parameter needed? If the named database have already been attached, SQL Server does not reattach it. It uses the attached database as the default for the connection.

See: connectionstrings.com