Limiting a sql query result with join and conditions

Question

I am writting a simple application that is ordering my medias (pictures, music, videos...). Each media can ben associated with 0 to many tags. My goal is to have a UI where I can search my medias (for exemple, show images and videos tagged like %hol%, and return both holidays tagged photos and hollywood tagged photos).

Here's my database :

Table medias
+---------+--------------+------+-----+---------+----------------+
| Field   | Type         | Null | Key | Default | Extra          |
+---------+--------------+------+-----+---------+----------------+
| id      | int(11)      | NO   | PRI | NULL    | auto_increment |
| path    | varchar(400) | NO   | UNI | NULL    |                |
| type    | varchar(5)   | NO   |     | NULL    |                |
| libelle | varchar(200) | NO   |     | NULL    |                |
| ratings | int(2)       | NO   |     | NULL    |                |
+---------+--------------+------+-----+---------+----------------+

Table tags
+---------+--------------+------+-----+---------+----------------+
| Field   | Type         | Null | Key | Default | Extra          |
+---------+--------------+------+-----+---------+----------------+
| id      | int(11)      | NO   | PRI | NULL    | auto_increment |
| libelle | varchar(200) | NO   | UNI | NULL    |                |
+---------+--------------+------+-----+---------+----------------+

Table medias_tags
+----------+---------+------+-----+---------+-------+
| Field    | Type    | Null | Key | Default | Extra |
+----------+---------+------+-----+---------+-------+
| id_media | int(11) | NO   | PRI | NULL    |       |
| id_tag   | int(11) | NO   | PRI | NULL    |       |
+----------+---------+------+-----+---------+-------+

As I have many medias, I had to limit the result. So in my front-end, I made a pagination system, and query my medias according to the page I am (for exemple, if I am on page 3, I put LIMIT 20 OFFSET 60 in my sql statement).

Now I'm trying to filter my medias. I have a searchbar, and if I type 'hol', I want to get 20 medias with tagged like '%hol%' (holidays, hollywood...)

Getting filtered medias works, but I don't know how to get exactly 20 medias.

Here's my sql query without filtering:

SELECT 
medias.id, medias.path, medias.type, medias.libelle as libelle, medias.ratings, tags.libelle as tag
FROM (select * from medias LIMIT ? OFFSET ?) medias 
left outer join medias_tags on medias.id = medias_tags.id_media 
left outer join tags on tags.id = medias_tags.id_tag

And here's my filtering sql query:

SELECT 
medias.id, medias.path, medias.type, medias.libelle as libelle, medias.ratings, tags.libelle as tag
FROM medias 
left outer join medias_tags on medias.id = medias_tags.id_media 
left outer join tags on tags.id = medias_tags.id_tag
WHERE tags.libelle LIKE ? [OR tags.libelle LIKE ? ...]

(last parameters are my tags)

Both query work well, but I can't find a way to limit my filtered result. Here's a sample of my filtering query result :

+----+-------------+-------+-------------------+---------+------------+
| id | path        | type  | libelle           | ratings | tag        |
+----+-------------+-------+-------------------+---------+------------+
| 11 | mock/02.jpg | PHOTO | 02.jpg            |       0 | dark       |
|  1 | mock/03.jpg | PHOTO | Purple            |       5 | wallpapper |
|  3 | mock/01.jpg | PHOTO | Wave              |       5 | wave       |
|  3 | mock/01.jpg | PHOTO | Wave              |       5 | wallpapper |
+----+-------------+-------+-------------------+---------+------------+

How can I limit my filtering result to only return n different medias id ? Is there a pure sql solution ? Maybe with stored procedures ?

Thanks !

EDIT :

Here's a result I'd like with limit = 7 :

+----+-------------+-------+-------------------+---------+------------+
| id | path        | type  | libelle           | ratings | tag        |
+----+-------------+-------+-------------------+---------+------------+
| 11 | mock/02.jpg | PHOTO | 02.jpg            |       0 | dark       |
|  7 | mock/01.jpg | PHOTO | NEWLY ADDED MEDIA |       8 | wallpapper |
|  2 | mock/02.jpg | PHOTO | Night             |       5 | wallpapper |
|  2 | mock/02.jpg | PHOTO | Night             |       5 | dark       |
|  1 | mock/03.jpg | PHOTO | Purple            |       5 | wallpapper |
|  4 | mock/03.jpg | PHOTO | Purple 2          |       5 | wallpapper |
|  5 | mock/03.jpg | PHOTO | Purple 3 EDITED   |       8 | wallpapper |
|  3 | mock/01.jpg | PHOTO | Wave              |       5 | wave       |
|  3 | mock/01.jpg | PHOTO | Wave              |       5 | wallpapper |
+----+-------------+-------+-------------------+---------+------------+

I have 9 rows, but only 7 distincts media id. Every media has a tag like '%a%'.

EDIT 2 : someone posted an answer, but deleted it. His idea was to concatenate tags, which would be a nice solution too.

Something like that :

+----+-------------+-------+-------------------+---------+------------+
| id | path        | type  | libelle           | ratings | tag        |
+----+-------------+-------+-------------------+---------+------------+
| 11 | mock/02.jpg | PHOTO | 02.jpg            |       0 | dark       |
|  7 | mock/01.jpg | PHOTO | NEWLY ADDED MEDIA |       8 | wallpapper |
|  2 | mock/02.jpg | PHOTO | Night             |       5 | wallpapper, dark |
|  1 | mock/03.jpg | PHOTO | Purple            |       5 | wallpapper |
|  4 | mock/03.jpg | PHOTO | Purple 2          |       5 | wallpapper |
|  5 | mock/03.jpg | PHOTO | Purple 3 EDITED   |       8 | wallpapper |
|  3 | mock/01.jpg | PHOTO | Wave              |       5 | wave, wallpapper       |
+----+-------------+-------+-------------------+---------+------------+

But I have no idea how to write this sql query...

Answer 1

Use GROUP_CONCAT in order to build a tag string per media and outer join this result. Then apply your limit clause as desired

select 
  medias.id, 
  medias.path, 
  medias.type, 
  medias.libelle, 
  medias.ratings,
  mtags.tags
from medias 
left outer join 
(
  select id_media, group_concat(tags.libelle order by tags.libelle) as tags
  from medias_tags
  join tags on tags.id = medias_tags.id_tag
  group by id_media
) mtags on mtags.id_media = medias.id
order by medias.id
limit 20 offset 60;

Answer 2

Are you expecting like this?

SELECT 
medias.id, medias.path, medias.type, medias.libelle as libelle, medias.ratings, tags.libelle as tag
FROM medias 
left outer join medias_tags on medias.id = medias_tags.id_media 
left outer join tags on tags.id = medias_tags.id_tag
WHERE tags.libelle LIKE ? [OR tags.libelle LIKE ? ...]
order by medias.id
limit 0,10

Here limit is used for first 10 record. you can use stored procedure for passing the two params of limit and pick the filtered result