Question

给出一个像这样的销售表：

| PRODUCT_ID | USER_ID |
|------------|---------|
|          1 |       1 |
|          2 |       1 |
|          3 |       1 |
|          3 |       2 |
|          4 |       2 |
|          1 |       3 |
|          3 |       3 |

与产品和制造商的表格如下：

| PRODUCT_ID | MANUFACTURER_ID |
|------------|-----------------|
|          1 |               1 |
|          2 |               1 |
|          3 |               2 |
|          4 |               2 |

如何找到从制造商处购买所有产品的用户？我知道我可以使用

SELECT *
FROM product
WHERE MANUFACTURER_ID = x

查找哪些产品属于制造商x，但我不知道如何从那里继续。

Answer 1

这将选择所有用户，其中某个制造商的产品尚未购买 - 因此他们已经购买了该制造商的所有产品。

select t1.user_id from (
    select user_id from sales s 
    join manufacturers m on s.product_id = m.product_id
    where manufacturer_id = x
    group by user_id
) t1 where not exists (
    select 1 from manufacturers m
    left join sales s on s.product_id = m.product_id and s.user_id = t1.user_id
    where m.manufacturer_id = t1.manufacturer_id       
    and s.product_id is null    
)

修改

另一种方法是选择已购买所有产品的所有用户

select t1.user_id from (
    select s.user_id, count(*) cnt from product p
    join sales s on s.product_id = p.product_id
    where p.manufacturer_id = x
    group by s.user_id
) t1 join (
    select count(*) cnt from product 
    where manufacturer_id = x
) t2 on t2.cnt = t1.cnt

Answer 2

我会写这样的查询：

select s.user_id
from sales s join
     products p
     on s.product_id = p.product_id
where p.manufacturer_id = x
group by s.user_id
having count(distinct s.product_id) = (select count(*)
                                       from products
                                       where manufacturer_id = x
                                      );

检查select语句中的多个值

2 个答案: