Make the query such a way that you don't have to write another one. For example,
SELECT * FROM User WHERE Email = @email and Password = @password
This would return all the records that has matched criteria.
Now, on Button_Click or any event of the control,
SqlCommand cmd= new SqlCommand("your query", connectionObject);
SqlDataAdapter da = new SqlDataAdapter(cmd);
DataTable dt = new DataTable();
da.Fill(dt);
userGridView.DataSource = dt;
userGridView.DataBind();
You can manipulate this code as per your requirements. This is just the basic idea how you can deal with your problem.
Hope this much is clear to you.
-KR