Mysql WHERE X同时匹配Y和Z

Question

I have 3 tables for storing images, tags and a link between the two. The structure is like this:

Table - photos

pid     name
--------------
1       image1
2       image2
3       image3
4       image4

Table - tags

tagID   tagName
---------------
1       red
2       blue
3       yellow
4       green

Table - photo_tag_bridge

pid     tagID
-------------
1       1
2       1
3       1
1       2
1       3

I want to create a SELECT statement to retrieve only the rows from 'photos' which match multiple 'tagID's. I've currently got this to try and bring back just image1 as it matches tagID 1 and 2

SELECT photos.pid
, photo_tag_bridge.pid, photo_tag_bridge.tagID
, tags.tagID 
FROM photos
, photo_tag_bridge
, tags 
where photos.pid = photo_tag_bridge.pid 
AND photo_tag_bridge.tagID = 1 
AND photo_tag_bridge.tagID = 2 
GROUP BY photos.pid

This doesn't bring anything back and it seems i may need to use an INNER JOIN?

Answer 1

There's 2 obvious solutions. One is to join to 2 instances of photo_tag_bridge (and two instances of tags if you were actually using any data from this table ):

SELECT photos.pid
FROM photos
, photo_tag_bridge ptb_a
, photo_tag_bridge ptb_b
WHERE photos.pid = ptb_a.pid 
AND photos.pid = ptb_b.pid 
AND ptb_a.tagID = 1 
AND ptb_b.tagID = 2 

Or you do an aggregate matching the DISTINCT count to the number of required matches (which is handy to match, for example, any 2 of 3 tags):

SELECT photos.pid
FROM photos
, photo_tag_bridge ptb
WHERE photos.pid = ptb_a.pid 
AND photos.pid = bptb_b.pid 
AND ptb.tagID IN (1,2) 
GROUP BY photos.pid
HAVING COUNT(DISTINCT ptb.tagID)=2;

Answer 2

As for my understanding, you need to get photo id which has multiple tags.

 create table #photo(id int,name varchar(10))
 create table #phototag(pid int,tgid int)
 create table #tag(id int,name varchar(10))

 select p.id,p.name from #photo p inner join #phototag pt on pt.pid=p.id group by p.id,p.name having count(*)>1