行转列例子：
select * from grade
select student ,max(decode(subject,'en',grade,null)) 英语 ,max(decode(subject,'ch',grade,null)) 语文,
max(decode(subject,'ma',grade,null)) 数学 from grade group by student
列转行：
创建测试表
create table test as
select student ,max(decode(subject,'en',grade,null)) 英语 ,max(decode(subject,'ch',grade,null)) 语文,
max(decode(subject,'ma',grade,null)) 数学 from grade group by student
select * from test
select student,'英语' 科目,英语 from test
union all
select student,'语文' 科目,语文 from test
union all
select student,'数学' 科目,数学 from test
