在oracle中构建虚拟列rowid
表:
`
CREATE TABLE `stack`
(`year` int(11) DEFAULT NULL,
`id` varchar(10) DEFAULT NULL,
`rate` float DEFAULT NULL)
ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
`
数据:
insert into stack values(2006,'p01',8);
insert into stack values(2001,'p01',5.9);
insert into stack values(2007,'p01',5.3);
insert into stack values(2009,'p01',4.4);
insert into stack values(2001,'p02',12.5);
insert into stack values(2004,'p02',12.4);
insert into stack values(2005,'p01',2.1);
insert into stack values(2000,'p01',0.8);
insert into stack values(2002,'p02',12.2);
insert into stack values(2002,'p01',3.9);
insert into stack values(2004,'p01',3.5);
insert into stack values(2003,'p02',10.3);
insert into stack values(2000,'p02',8.7);
insert into stack values(2006,'p02',4.6);
insert into stack values(2007,'p02',3.3);
insert into stack values(2003,'p01',7.4);
insert into stack values(2008,'p01',6.8);
像这样的SQL:
select t3.year,t3.id,t3.rate
from (select t1.*, (select count(*) from stack t2 where t1.rate<=t2.rate and t1.id=t2.id) as rownum from stack t1) t3
where rownum <=3 order by id,rate DESC;
如果删除t3中的where子句,则显示如下:
获取“前n个记录”->在where子句(t3的where子句)中添加“rownum<=3”;
选择“年份”->在where子句(t3的where子句)中添加“2000到2009之间”;
