正在寻找解决此sql查询的更优雅的方法

我得到了一个具有

产品：

maker   model   type
A   1232    PC
A   1233    PC
A   1276    Printer
A   1298    Laptop
A   1401    Printer
A   1408    Printer
A   1752    Laptop
B   1121    PC
B   1750    Laptop
C   1321    Laptop
D   1288    Printer
D   1433    Printer
E   1260    PC
E   1434    Printer
E   2112    PC
E   2113    PC

问题是

找到只生产一种产品类型和多种产品的制造商 模型

输出列应为maker和type

这就是我想到的

select distinct maker, type
from Product
where maker in (select maker
                from Product
                group by maker, type
                having count(model) > 1
                except
                select maker
                from 
                (
                    select distinct maker, type
                    from Product
                ) A
                group by maker
                having count(type) > 1)

我知道这看起来并不优雅，所以我想知道是否有人能想出一个更好的选择，并解释为什么它比上面提到的查询更好

---

编辑：请确保答案仅为两栏宽，即

---

制造商，类型

一种方法使用

存在

和

不存在

：

select count(distinct model) as unique_model_count,
       count(distinct type) as unique_type_count,
       maker
from Product
group by maker
having unique_type_count=1 and unique_model_count>1

select distinct p.maker, p.type
from product p
where exists (select 1
              from product p2
              where p2.maker = p.maker and p2.type = p.type and p2.model <> p.model
             ) and
      not exists (select 1
                  from product p2
                  where p2.maker = p.maker and p2.type <> p.type
                 );

---

你能为你的RDBMS引擎添加一个标签吗？子查询可以是一个GROUP BY，带有条件。这肯定是一个“正确”的答案！但是，我认为“制造商”和“类型”都需要包括在内；这里显示的内容的简单修复。（没有尝试过…）我不是100%确定列名是否可以如“Having”子句中所示使用，但可能必须在此处重复“count（）”表达式。？逻辑正确，但如果未指定的RDBMS不允许having子句中使用别名，则可能引发错误。@MikeRobinson。我认为这不是正确的答案，因为它不包括

类型

。在大多数数据库中，这将返回一个错误（

类型

未开始聚合）。在MySQL中，每个maker只返回一个

类型

。我知道，但问题是哪个maker会生成一个类型，所以我认为它可以

select p.maker, p.type
from product p
where not exists (select 1
                  from product p2
                  where p2.maker = p.maker and p2.type <> p.type
                 )
group by p.maker, p.type
having min(model) <> max(model);

select p.model, p.type
from (select p.*,
             min(type) over (partition by maker) as mintype,
             max(type) over (partition by maker) as maxtype,
             row_number() over (partition by maker, type order by model) as seqnum,
             count(*) over (partition by maker, type) as cnt
      from product p
     ) p
where seqnum = 1 and
      mintype = maxtype and
      cnt > 1;

SELECT maker, MIN(type) as type
FROM Product
GROUP BY maker
HAVING COUNT(DISTINCT type) = 1 AND COUNT(DISTINCT model) > 1;