ORACEL的分析函数：可以取出分组中第一个（最后一个）的数据
first_value() over(partition by ... order by ...)
last_value() over(partition by ... order by ...)
create table ATEM
(
CO1 VARCHAR2(10),
CO2 INTEGER
)
insert into atem(co1,co2) values('a',1);
insert into atem(co1,co2) values('a',2);
insert into atem(co1,co2) values('a',3);
insert into atem(co1,co2) values('a',4);
insert into atem(co1,co2) values('a',1);
insert into atem(co1,co2) values('b',1);
insert into atem(co1,co2) values('b',2);
insert into atem(co1,co2) values('c',1);
insert into atem(co1,co2) values('d',1);
insert into atem(co1,co2) values('d',2);
select distinct(FIRST_VALUE(a.co2)OVER(PARTITION BY a.co1 ORDER BY a.co2)) as co2,a.co1
from atem a
// FIRST_VALUE(a.co2)OVER(PARTITION BY a.co1 ORDER BY a.co2)
//在表中以a.co1分组，并在分组中以a.co2排序，最后要得到分组中a.co2的数据
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