Retrieve Values from Db by passing parameter from previous Page - ASP.NET C# -

i new asp.net,

i having issue retrieving employee information db when passing userid previous page. have managed pass userid when selected data grid in page 1 when loading page 2 gives me error: invalid column name 'value of string passed'

below code:

page 1:

protected void imgbtnview_click(object sender, imageclickeventargs e)

{         imagebutton imgbtn = (imagebutton)sender;         string userid = imgbtn.commandargument;         response.redirect("employee.aspx?userid=" + userid); } 

page 2 :

page load

protected void page_load(object sender, eventargs e) {         txtemployeeno.text = request.querystring["userid"];     fillfields(txtemployeeno.text); } 

method fillfields

private void fillfields(string user_id) {     string commandstring = @"select * [dbo].[tbl_employee]      [userid] = "+ user_id;     datarow dr = global.startquery(commandstring).rows[0]; -- > global class     txtemployeeno.text = user_id;     txtfirstname.text = dr["firstname"].tostring();      txtlastname.text =  dr["lastname"].tostring(); } 

please tell me what's wrong in code.

thank in advance

user following line of code.

string commandstring = @"select * [dbo].[tbl_employee]  [userid] = '"+user_id+"'";