条件写在前面

string sqlrequirement ="";

if(dtp_sta.text==""&&dtp_end.text=="")

{

　　sqlrequirement=""

} else if(dtp_sta.text!=""&&dtp_end.text!="")

{

　　sqlrequirement=" and date >"+dtp_sta.text + " and date <" +dtp_end.text;

}

string sql = "select * from table1 where id >99 " + sqlrequirement;