--是这样一个问题，数据库中的字段有  year, month, supermarkname,salesNumber.四个字段。如何编写SQL语句使得查询出来的结果如下

year   supermarkName   1月   2月    3月    4月     5月     。。。    （列名）
2012     超市1              500   300   200   100    200     。。。    (查询出的结果)

drop table sales;

create table sales
(
year char(4),
supermarkname varchar2(20),
month varchar2(10),
salesnumber number(5)
)
/

insert into sales values('2012','超市1','1月',500);
insert into sales values('2012','超市1','2月',300);
insert into sales values('2012','超市1','3月',200);
insert into sales values('2012','超市1','4月',100);
insert into sales values('2012','超市1','5月',200);
insert into sales values('2012','超市1','6月',600);
insert into sales values('2012','超市2','1月',500);
insert into sales values('2012','超市2','2月',300);
insert into sales values('2012','超市2','3月',200);
insert into sales values('2012','超市2','4月',100);
insert into sales values('2012','超市2','5月',200);
insert into sales values('2012','超市2','6月',600);
insert into sales values('2013','超市1','1月',500);
insert into sales values('2013','超市1','2月',300);
insert into sales values('2013','超市1','3月',200);
insert into sales values('2013','超市1','4月',100);
insert into sales values('2013','超市1','5月',200);
insert into sales values('2013','超市1','6月',600);

commit;

--decode查询语句，实现行转列
select YEAR,SUPERMARKNAME,
sum(decode(month,'1月',salesnumber,0)) "1月",
sum(decode(month,'2月',salesnumber,0)) "2月",
sum(decode(month,'3月',salesnumber,0)) "3月",
sum(decode(month,'4月',salesnumber,0)) "4月",
sum(decode(month,'5月',salesnumber,0)) "5月",
sum(decode(month,'6月',salesnumber,0)) "6月",
sum(decode(month,'7月',salesnumber,0)) "7月",
sum(decode(month,'8月',salesnumber,0)) "8月",
sum(decode(month,'9月',salesnumber,0)) "9月",
sum(decode(month,'10月',salesnumber,0)) "10月",
sum(decode(month,'11月',salesnumber,0)) "11月",
sum(decode(month,'12月',salesnumber,0)) "12月"
from sales group by YEAR,SUPERMARKNAME;