primary and foreign key problem

I am using ASP.NET 4.0 and SQL server 2008 R2 in my project. I have used membership provider for creating user.I have taken the primary key (UserId) from aspnet_Users table as a foreign key (u_id) in JUWUser table.
Now the problem is that I have to insert the user id from the primary key column to the foreign key column. I have tried using select and insert statement, but it is not working.
I am retrieving the value from the database in my label so that I can insert the id in its right place.

Following is my code:

{
	lblname.Text = Convert.ToString(Session["name"]);
	string myConnectionString = @"Data Source=(local);Initial Catalog=PortalDB;Integrated Security=True";

	SqlCommand cmd2 = new SqlCommand("select UserName from JUWUser", new SqlConnection(myConnectionString));
	cmd2.Connection.Open();
	lblcmpr.Text = cmd2.ExecuteScalar().ToString();


	if (lblname.Text == lblcmpr.Text)
	{
		SqlCommand cmd = new SqlCommand("select UserId from aspnet_Users where UserName ='" + lblname.Text + "'", new SqlConnection(myConnectionString));
		cmd.Connection.Open();
		lblID.Text = cmd.ExecuteScalar().ToString();
		SqlCommand cmd1 = new SqlCommand("insert into JUWUser(u_id) values ('" + lblID.Text + "')", new SqlConnection(myConnectionString));
		cmd1.Connection.Open();
		cmd1.ExecuteScalar().ToString();
		cmd.Connection.Close();
		cmd1.Connection.Close();
	}
	else
		lblID.Text = "error";
}

This is the code of profile page.
In this code lblname is storing value from a session variable which contains the Username of the User that has logged in.
lbl cmpr is retrieving all the values from UserName column in the JUWUser table.
lblID is retrieving the ID from the aspnet_Users table where the UserName column value in aspnet_Users matches the value in lblname.text.

Now I have to insert this id in JUWUser table in u_id column where the UserName matches lblname.text

An insert and where statement cannot come together.

How should I do this?

Please Help

Tags: C# (C# 4.0), ASP.NET, SQL Server