SQL分組多列統計(GROUP BY后按條件分列統計) -轉

今天在園子里看到個group by 分組多列統計的例子，轉走給大家分享一下：

create table tests (year datetime year to year,type char(1),value int);
alter table tests alter colomn year int;

insert into tests values (2015,1,100);
insert into tests values (2015,2,200);
insert into tests values (2016,1,150);
insert into tests values (2016,2,300);
insert into tests values (2016,3,100);

YEAR	TYPE	VALUE
2015	1	100
2015	2	200
2016	1	150
2016	2	300
2016	3	100

 

 

 

 

 

轉為：

YEAR	TYPE1	TYPE2	TYPE3
2015	100	200	0
2016	150	300	100

 

 

 

 

這時候我們除了用到GROUP BY之外還需要CASE WHEN，SQL如下：

SELECT year,
 SUM(CASE WHEN type=1 THEN value ELSE 0 END) as type1,
 SUM(CASE WHEN type=2 THEN value ELSE 0 END) as type2,
 SUM(CASE WHEN type=3 THEN value ELSE 0 END) as type3,
 FROM table_test GROUP BY year