php-在微信mysql中想实现：当记录不存在时insert,当

if($keyword==1||$keyword==2){            $sql_insert="INSERT INTO `760827`.`session` (`id`,`openid`,`status`) VALUES ('','$fromUsername','$keyword');";            $sql_update="UPDATE  `760827`.`session` SET  `status` =  '$keyword' WHERE  `session`.`openid` =$fromUsername;";            $sql_yanzheng="SELECT * FROM `760827`.`session` WHERE 'openid'=$fromUsername;";            $result_yanzheng=mysql_query($sql_yanzheng,$conn);            if($keyword==1){                if(mysql_num_rows($result_yanzheng) > 0){                    $reply="update";                    echo _response_text($reply);                      //mysql_query($sql_update,$conn);                }                elseif(mysql_num_rows($result_yanzheng) == 0){                    $reply="insert";                //和下面的echo构成微信输出函数                    echo _response_text($reply);                        //mysql_query($sql_insert,$conn);                }                               }            elseif($keyword==2){                if(mysql_num_rows($result_yanzheng) > 0){                    mysql_query($sql_update,$conn);                }                else{                    mysql_query($sql_insert,$conn);                }            $reply="请输入您的留言：";            echo _response_text($reply);            }        }