select * from (
select
class 班級,
subject,
avg(grade) avg_grade
from student_score
group by class,subject
)
pivot (sum(avg_grade) for subject in ('語文', '數學','英語')) order by 班級 asc
求班級平均分
select 學科,平均分 別名 from 表
where class="121"
就是group by 班級,平均分
1.121班的平均分
2.行轉列
由於2的結果並沒有班級這個字段，'121' 班級 湊字段（湊維度）
t121.*就是子查詢。 查詢t121表的所有字段
3.湊維度
4.聯合查詢union
最終代碼：
select '121' 班級,t121.* from (
select * from(
select subject,avg(grade) avg_grade from student_score
where class="121"
group by class,subject
)
pivot (sum(avg_grade) for subject in ('語文', '數學','英語'))
)t121
union
select '122' 班級,t122.* from (
select * from (
select subject,avg(grade) avg_grade from student_score
where class="122"
group by class,subject
)
pivot (sum(avg_grade) for subject in ('語文', '數學','英語'))
)t122