如何使用 group by 从表中计算 Max(Count(Columnname))

Question

如何查找以下查询的数据

Original Source第89题

表结构： 产品（制造商、型号、类型）

编辑 Use sqlfiddle for schema

任务：
找出那些拥有最多模型的制造商 产品表以及模型数量最少的那些。 输出：制造商、模型数量

有问题的提示是GROUP BY、HAVING 和IN

我尝试了各种方法来找到这个基本上我想出的是我需要使用Max(COUNT(model))

结果应该是

maker   qty 
A        7 --max
C        1 --min

我想出的一个解决方案是

select maker, count(ps.model) as Count from product as ps
group by ps.maker
having count(ps.model) in
(
select max(cnt) from (select count(model) as cnt from product group by maker)t
union
select min(cnt) from (select count(model) as cnt from product group by maker)t
)

还有没有其他办法。

Answer 1

你可以简单...

SELECT *
FROM (
    SELECT TOP 1 maker, COUNT(*) C
    FROM product
    GROUP BY maker
    ORDER BY C DESC
) Q1
UNION
SELECT *
FROM (
    SELECT TOP 1 maker, COUNT(*) C
    FROM product
    GROUP BY maker
    ORDER BY C
) Q2;

...或者如果您喜欢 CTE...

WITH CTE AS (
    SELECT maker, COUNT(*) C
    FROM product
    GROUP BY maker
)
SELECT *
FROM (
    SELECT TOP 1 *
    FROM CTE
    ORDER BY C DESC
) Q1
UNION
SELECT *
FROM (
    SELECT TOP 1 *
    FROM CTE
    ORDER BY C
) Q2;

...正如SQL Fiddle 中所展示的那样。

Answer 2

如果您使用的是 SQL Server 2008，您可以通过以下方式对其进行简化：http://www.sqlfiddle.com/#!3/25ba8/7

with counts as
(
  select maker, count(ps.model) as Count from product as ps
  group by ps.maker
)
select cx.*
from counts cx
join
(
  select min(count) as lo, max(count) as hi
  from counts
) as hi_lo 
on cx.count = hi_lo.lo or cx.count = hi_lo.hi;