MySQL query to search for items with certain tags

问题

I have a MySQL database with the following tables:

items      | id, item
items_tags | id, item_name, item_id, tag_name, tag_id
tags       | id, tag

I'd like to allow the user to search for items with any tag or any combination of tags. Here's some example data to show what I'd like to do:

items:

id | item
-----------
1  | banana
2  | orange
3  | tomato

items_tags:

id | item_name | item_id | tag_name | tag_id
---------------------------------------------
1  | banana    | 1       | yellow   | 1
2  | banana    | 1       | fruit    | 2
3  | orange    | 2       | orange   | 3
4  | orange    | 2       | fruit    | 2
5  | tomato    | 3       | red      | 4
6  | tomato    | 3       | vegetable| 5    

tags:

id | tag
--------------
1  | yellow
2  | fruit
3  | orange
4  | red
5  | vegetable

What query could I run to only return items tagged with "yellow" and "fruit" (i.e., should return row 1 of items)?

Thanks!

UPDATE:

Here's the working answer:

SELECT * 
  FROM items 
 WHERE id IN (
              SELECT item_id
                FROM items_tags
               WHERE tag_name IN ('yellow', 'fruit')
            GROUP BY item_id
              HAVING COUNT(*) = 2
             )

Thanks to chetan for the help!

回答1:

if you want the item with any of the two tag then:

select distinct item_id, item_name 
from items_tags 
where tag_name in ('yellow', 'fruit'); 

if you want the item having both tag then:

select item_id, item_name 
from items_tags 
where tag_name id ('yellow', 'fruit')
group by item_id, item_name
having count(*) = 2; 

based on your comment

  select a.id, a.item 
    from items a, items_tags b, tags c 
   where a.id = b.item_id
     and b.tag_id = c.id
group by id, item
  having (group_concat(c.tag) like '%yellow%' 
         and  group_concat(c.tag) like '%fruit%')
      or group_concat(c.tag) = 'red';

This query gives id and item from items table. It gives item which has both yellow and fruit tag. and the items with only red tag.

if you want to get items with two tags and only two tags then use following condition in having clause

(group_concat(c.tag) like '%yellow%' 
and group_concat(c.tag) like '%fruit%'
and count(*) = 2) 

回答2:

Try this::

    Select *, count(1) as noOfTags from 
    items_tags
 group by item_id 
having  tag_name in ('yellow','fruit') and  noOfTags=2

回答3:

   Select *, count(1) as noOfTags from 
    items_tags
 group by item_id 
having  tag_name in ('yellow','fruit') and  noOfTags=2

yes noofTags here make sure that the item is tagged with all tags, and yes if you want to search for more tags you will add it between parentheses Another Thing i agree with Mark about his comment,they are useless & you can use view instead it you want to get something like that (At least save some space). Note : I can't comment yet so i posted like answer sorry.

来源：https://stackoverflow.com/questions/17519718/mysql-query-to-search-for-items-with-certain-tags