Read just one row (primary key) and display each column of the row

[DeafSmith]

I am using Postgresql in VS 2013 and C#.

I use this for the reading of just one row by primary key.

string p has the users id it must look for in the table.

 cn.Open();
 selectSql = "SELECT user_id,user_name,user_password,user_administrator FROM userlogon WHERE user_id ='" + p + "'";
 cmd.CommandText = selectSql;
 NpgsqlDataAdapter da = new NpgsqlDataAdapter(selectSql, conn);
 NpgsqlCommandBuilder cdb = new NpgsqlCommandBuilder(da);
 DataSet ds = new DataSet();
 DataTable dt = new DataTable();
 ds.Reset();
 da.Fill(ds);                 
 dt = ds.Tables[0];

I now want the first column of the row to be moved to another string like:

got_userID = dt.Columns[0].ToString();

But all I get is literally the field's name, 'user_id' in got_userID when I display it via messageBox.Show !

Any idea why?

Thanks!