How to save XML data in SQL Server? -

in table there 1 xml column. want fetch xml data in 1 textbox , make corrections , update it:

private void button2_click(object sender, eventargs e) {      con.open();      string str = "select c1 tablename c2='" + txt1.text+ "'";       sqlcommand cmd1 = new sqlcommand(str, con);      xmlreader xml = cmd1.executexmlreader();      xml.read();       txt2.text = xml.readouterxml();       xmldocument doc = new xmldocument();      doc.preservewhitespace = true;      doc.loadxml(txt2.text); } 

now want make changes , update in database. when try change in textbox not work. how can make changes , update in database? please help

update

using (sqlconnection connection = new sqlconnection(connectionstring)) using (sqlcommand command = connection.createcommand()) {  command.commandtext = "update tablename set  c1 =  @c1 c2 = @c2 "; command.parameters.addwithvalue("@c1", textbox2.text); command.parameters.addwithvalue("@c2", textbox1.text); connection.open(); command.executenonquery(); connection.close(); }