public static bool UpdateNew(Entity.PW_User NewUser)
        {
            try
            {
                Entity.PW_User tt = NewUser;
              
                StringBuilder sb = new StringBuilder();
                sb.Append(" update pw_User set ");
                sb.Append(" UserName=:UserName, ");
                sb.Append(" Password=:Password, ");
                sb.Append(" UserGroupCode=:UserGroupCode, ");
                sb.Append(" CreateTime=:CreateTime, ");
                sb.Append(" LastLoginTime=:LastLoginTime  ");
                sb.Append(" where UserID=:UserID ");
                //Oracle里的command 要在参数名前用冒号:标注。SqlServer和MySQL都是用@。
                //见-----http://www.codeproject.com/Questions/618582/ORA-00936-missing-expression
                OracleCommand cmd = new OracleCommand();
                cmd.CommandText = sb.ToString();
                cmd.CommandType = CommandType.Text;
                //下面添加参数的顺序一定要跟上面的语句里各参数出现的顺序一致。否则更新不成功。
                //如下面的UserID参数不能先于前面5个参数的任何一个出现。
                cmd.Parameters.Add(new OracleParameter("UserName", OracleDbType.NVarchar2, 45) { Value = tt.UserName });
                cmd.Parameters.Add(new OracleParameter("Password", OracleDbType.Varchar2, 45) { Value = tt.Password });
                cmd.Parameters.Add(new OracleParameter("UserGroupCode", OracleDbType.Varchar2, 45) { Value = tt.UserGroupCode });
                cmd.Parameters.Add(new OracleParameter("CreateTime", OracleDbType.Varchar2, 45) { Value = tt.CreateTime });
                cmd.Parameters.Add(new OracleParameter("LastLoginTime", OracleDbType.Varchar2, 45) { Value = tt.LastLoginTime });
                cmd.Parameters.Add(new OracleParameter("UserID", OracleDbType.Varchar2, 50) { Value = tt.UserID });

                int val = DBHelper_Oracle. ExecuteNonQuery(cmd);

                if (val > 0)
                {
                    return true;
                }
                else
                {
                    return false;
                }

            }
            catch
            {
                return false;
            }
        }