给定一个数据库的表Test，表的内容如图所示。
| id | class | score |
| ------------- |:-------------:| -----:|
| 1 | one | 91 |
| 2 | one | 92 |
| 3 | two | 93 |
| 4 | two | 94 |
要求写出一个SQL语句，得到如下的结果。
| one | two |
|---|---|
| 2 | 2 |
思路
select class, count(*) from Test group by class
得到
| one | 2 |
| two | 2 |
再行转列
with t1 as (
select class, count(*) as num from Test group by class
)
select
sum(case class when 'one' then num else 0 end) as one,
sum(case class when 'two' then num else 0 end) as two
from t1
方法二：
select
sum(case class when 'one' then 1 else 0 end) as one,
sum(case class when 'two' then 1 else 0 end) as two
from Test
方法三：
SELECT * FROM
(
select class, count(*) as num from Test group by class
) t
PIVOT (
SUM(num)
FOR class IN ([one],[two])
) p