SQL分组多列统计(GROUP BY后按条件分列统计) -转

今天在园子里看到个group by 分组多列统计的例子，转走给大家分享一下：

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);

转为：

这时候我们除了用到GROUP BY之外还需要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