sql计算当前年较上一年的销售量的增长率(当年的一道sql笔试题)

create table YEAR_SALES
(
  YEAR     VARCHAR2(4),
  QUANTITY NUMBER
)
;

prompt Loading YEAR_SALES...
insert into YEAR_SALES (YEAR, QUANTITY)
values ('2001', 100);
insert into YEAR_SALES (YEAR, QUANTITY)
values ('2002', 200);
insert into YEAR_SALES (YEAR, QUANTITY)
values ('2003', 220);
insert into YEAR_SALES (YEAR, QUANTITY)
values ('2004', 260);
insert into YEAR_SALES (YEAR, QUANTITY)
values ('2005', 300);
insert into YEAR_SALES (YEAR, QUANTITY)
values ('2006', 330);
commit;

select t1.year, t1.quantity / t2.quantity increase_rate
  from year_sales t1
 inner join year_sales t2 on t1.year - 1 = t2.year