标签：
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);
| YEAR | TYPE | VALUE |
| 2015 | 1 | 100 |
| 2015 | 2 | 200 |
| 2016 | 1 | 150 |
| 2016 | 2 | 300 |
| 2016 | 3 | 100 |
转为：
| YEAR | TYPE1 | TYPE2 | TYPE3 |
| 2015 | 100 | 200 | 0 |
| 2016 | 150 | 300 | 100 |
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
SQL分组多列统计(GROUP BY后按条件分列统计) -转
标签：
原文地址：http://www.cnblogs.com/sarahs/p/4435089.html
