Question

我有两张桌子：照片和photograph_tags。 Photograph_tags包含名为photograph_id的列（照片中的id）。一张照片可以有很多标签。我有一个与三个标签相关的照片行：男孩，溪流和水。但是，运行以下查询将返回0行

SELECT p.*
FROM photographs p, photograph_tags c
WHERE c.photograph_id = p.id
AND (c.value IN ('dog', 'water', 'stream'))
GROUP BY p.id
HAVING COUNT( p.id )=3

此查询有问题吗？

My tables look like so
-----------------------
photographs
-----------------------
id | title | location
------------------------
7  | asdf | c:\...


-----------------------
photograph_tags
-----------------------
id | photograph_id | value
1  | 7             | dog
2  | 7             | water
3  | 7             | stream
4  | 7             | mountains

I want to pull all photograph rows that relate to at least all three of the searched tags

Answer 1

使用您指定的3个标签（或更多）获取所有照片。从标签开始并加入照片。

select
 p.id
from photographs p

left join photograph_tags c
on p.id = c.photograph_id
and c.value IN ('dog', 'water', 'stream')

group by p.id

having count(c.value) >= 3

测试上面的代码：

create table #photograph_tags (
    photograph_id INT,
    value varchar(50)
)

create table #photographs (
    id int
)

insert into #photographs values (7)
insert into #photographs values (8)

insert into #photograph_tags values (7, 'dog')
insert into #photograph_tags values (7, 'water')
insert into #photograph_tags values (7, 'stream')
insert into #photograph_tags values (7, 'mountains')
insert into #photograph_tags values (8, 'stream')
insert into #photograph_tags values (8, 'mountains')

select * from #photographs
select * from #photograph_tags

select
    p.id
from #photographs p

left join #photograph_tags c
on p.id = c.photograph_id
and c.value IN ('dog', 'water', 'stream')

group by p.id

having count(c.value) >= 3


drop table #photograph_tags
drop table #photographs

Answer 2

SELECT p.* FROM photographs p join 
(select id, COUNT(id) as TagCount 
    FROM Photograph_Tags c
    WHERE c.value IN ('dog', 'water', 'stream')
    group by id) 
    as TagCounts on p.id = TagCounts.id
WHERE TagCount = 3

Answer 3

SELECT p。* 来自照片p 在哪里（c.value IN（'dog'，'water'，'stream'）） AND（选择计数（*）来自photograph_tags c
在哪里c.photograph_id = p.id）＆gt; = 3;

会给你带有至少三个标签的照片。

这个SQL查询有什么问题？

3 个答案: