如何查询多对多关系

Question

3 表： Fruits(id, name) Buckets(id, name) Bucket_Fruit(id, fruit_id, bucket_id, count)

例如有一个桶 Bucket1 有 2 个苹果和 1 个香蕉：

水果.id	水果名称
1	苹果
2	香蕉

桶.id	Buckets.name
1	桶 1

Bucket_Fruit.id	Bucket_Fruit.fruit_id	Bucket_Fruit.bucket_id	Bucket_Fruit.count
1	1	1	2
2	2	1	1

问题是：如何查询只有 2 个苹果和 1 个香蕉的桶？ 我可以保证不会有 2 个桶有相同的水果。

Answer 1

尝试这个：

select distinct bucket_id 
from Bucket_Fruit b
where exists (select * from Bucket_Fruit where bucket_id=b.bucket_id 
                                        and fruit_id=(select id from Fruits where name='apple') 
                                        and count=2)
    and exists (select * from Bucket_Fruit where bucket_id=b.bucket_id 
                                        and fruit_id=(select id from Fruits where name='banana') 
                                        and count=1)
    and bucket_id in (select bucket_id from Bucket_Fruit group by bucket_id having count(fruit_id)=2)
;