如何按特定标准进行分组和计数？

Question

我有一张桌子，上面放着汽车和车库。每辆车仅在一个车库中列出，但是一个车库中可以有很多车。我想知道车库中每种汽车有多少种。每辆车在数据库中都有自己的行。

这张桌子看起来像这样。

+-------+--------+-----+
|carType| garage |id   |
+-------+--------+-----+
| 1     | 1      | 1   |
+-------+--------+-----+
| 1     | 1      | 2   |
+-------+--------+-----+
| 1     | 2      | 3   |
+-------+--------+-----+
| 2     | 2      | 4   |
+-------+--------+-----+

这就是我想要的。

+-------+------------+--------+
|carType| carCount   | garage |
+-------+------------+--------+
| 1     | 2          | 1      |
+-------+------------+--------+
| 1     | 1          | 2      |
+-------+------------+--------+
| 2     | 1          | 2      |
+-------+------------+--------+

问题是我不知道查询的外观。

Answer 1

您只需要GROUP BY carType 和 garage：

SELECT carType, COUNT(*) AS carCount, garage
FROM cars
GROUP BY carType, garage

输出：

carType garage  carCount
1       1       2
1       2       1
2       2       1

Demo on dbfiddle

Answer 2

我第一次尝试回答这里的问题，希望它能解决问题！ 就像戈登所说的“提示分组依据”一样，如果在下面不正确，请大声疾呼戈登。

with t
as
(select * from(values(1,1,1),(1,1,2),(1,2,3),(2,2,4)) as t (carType,garage,id))

select carType, count(id) as carCount, garage
from t
group by carType, garage