查询各个学生的每一科的成绩与总分以及平均分（保留2位小数），并且按照成绩的平均分 进行倒序排序

需求

1. 查询各个学生的每一科的成绩与总分以及平均分（保留2位小数），并且按照成绩的平均分
   进行倒序排序，要求展示方式：

---

`
$data=array(
	'0'=>array(
	'id'=>'',
	's_id'=>'',
	'name'=>'',
	'sub1_score'=>0.0,
	'sub2_score'=>0.0,
	'sub3_score'=>0.0,
	'total_score'=>0.0,
	'avg_score'=>0.0
	),
	……
	'9'=>array(
	'id'=>'',
	's_id'=>'',
	'name'=>'',
	'sub1_score'=>0.0,
	'sub2_score'=>0.0,
	'sub3_score'=>0.0,
	'total_score'=>0.0,
	'avg_score'=>0.
	)
);`

原生SQL

` 
select s.id,s.s_id,s.name,
    	SUM(case c.name when 'IT0' then convert(g.score,decimal(5,2)) else 0 end) as 'IT0',
    	SUM(case c.name when 'IT1' then convert(g.score,decimal(5,2)) else 0 end) as 'IT1',
    	SUM(case c.name when 'IT2' then convert(g.score,decimal(5,2)) else 0 end) as 'IT2',
    	convert(sum(g.score)/3,decimal(5,2)) as '平均成绩',
    	convert(sum(score),decimal(5,2)) as total
    from student s,subject c,score g where s.s_id=g.s_id and c.id=g.sub_id
    	group by s.s_id order by sum(g.score) desc
`