- 行转列的常规做法是，group by+sum(if())【或count(if())】

例题：
已知

year	month	amount
1991	1	1.1
1991	2	1.2
1991	3	1.3
1991	4	1.4
1992	1	2.1
1992	2	2.2
1992	3	2.3
1992	4	2.4

查成这样一个结果

year	m1	m2	m3	m4
1991	1.1	1.2	1.3	1.4
1992	2.1	2.2	2.3	2.4

解答：

use test_sql;
set hive.exec.mode.local.auto=true;
create table table2(year int,month int ,amount double) ;
insert overwrite table table2 values(1991,1,1.1),(1991,2,1.2),(1991,3,1.3),(1991,4,1.4),(1992,1,2.1),(1992,2,2.2),(1992,3,2.3),(1992,4,2.4);
select * from table2;--行转列
--常规做法是，group by+sum(if())
--SQLserver中有pivot专门用来行转列
--原始写法
select year,sum(a) as m1,sum(b) as m2,sum(c) as m3,sum(d) as m4
from(select *,if(month=1,amount,0) a,if(month=2,amount,0) b,if(month=3,amount,0) c,if(month=4,amount,0) dfrom table2 ) t
group by t.year;
--简化写法
select year,,sum(if(month=1,amount,0)) m1,sum(if(month=2,amount,0)) m2,sum(if(month=3,amount,0)) m3,sum(if(month=4,amount,0)) m4
from table2
group by year;