字段数据相加求和,该怎么处理

$sql =<<< SQL
create table `学生成绩表` (
  `学号` int,
  `姓名` varchar(10),
  `语文` int default 0,
  `数学` int default 0,
  `英语` int default 0,
  `总分` int default 0,
  PRIMARY KEY (`学号`)
)
SQL;
//mysql_query($sql) or die(mysql_error());//执行一次后就注释掉

$sql = <<< SQL
insert into `学生成绩表` values 
(1, '张三', 65, 75, 80, 0),
(2, '李四', 60, 70, 80, 0),
(3, '王麻子', 68, 72, 85, 0)
SQL;
//mysql_query($sql) or die(mysql_error());//执行一次后就注释掉

//mysql_query('update `学生成绩表` set `总分`=`语文`+`数学`+`英语`');//执行一次后就注释掉

$sql =<<< SQL
select
 sum(`总分`) as `总分合计`, avg(`总分`) as `总平均分`,
 sum(`语文`) as `语文总分`, avg(`语文`) as `语文平均分`,
 sum(`数学`) as `数学合计`, avg(`数学`) as `数学平均分`,
 sum(`英语`) as `英语合计`, avg(`英语`) as `英语平均分`
 from `学生成绩表`
SQL;
$rs = mysql_query($sql) or die(mysql_error());
$row = mysql_fetch_assoc($rs);
print_r($row);