Question

I’m working on a tags system, what it should do is you can have a query and selected tags, e.g. jquery and tags of javascript, library. It should only show related scripts with the query AND only that have the tags. This is the database layout:

Scripts table:

+-----------+---------------+
| script_id | name          |
+-----------+---------------+
|         1 | jQuery        |
|         2 | Sencha Touch  |
|         3 | Codeigniter   |
|         4 | Google Chrome |
|         5 | memcached     |
|         6 | PHP           |
|         7 | MooTools      |
|         8 | node.js       |
|         9 | jQuery Mobile |
+-----------+---------------+

Tags table:

+--------+-------------+-------------+
| tag_id | name        | url_name    |
+--------+-------------+-------------+
|      1 | JavaScript  | javascript  |
|      2 | Library     | library     |
|      3 | PHP         | php         |
|      4 | MySQL       | mysql       |
|      5 | Cache       | cache       |
|      6 | HTML        | html        |
|      7 | Open source | open-source |
+--------+-------------+-------------+

Tagged table:

+-----------+--------+-----------+
| tagged_id | tag_id | script_id |
+-----------+--------+-----------+
|         1 |      1 |         1 |  # javascript -- jQuery
|         2 |      2 |         1 |  # library    -- jQuery
|         3 |      1 |         9 |  # javascript -- jQuery mobile
+-----------+--------+-----------+

When I run my SQL, it still picks up jQuery Mobile but it shouldn’t because it doesn’t contain the library tag where jQuery does, I need it to constrain results that must meet the tags selected.

This is my SQL:

SELECT scripts.script_id,
       scripts.name
FROM
(
    scripts scripts

    LEFT OUTER JOIN tagged tagged ON tagged.script_id = scripts.script_id

    LEFT OUTER JOIN tags tags ON tags.tag_id = tagged.tag_id
)
WHERE MATCH(scripts.name) AGAINST ('jquery*' IN BOOLEAN MODE) AND ( tags.url_name = 'javascript' OR tags.url_name = 'library' )
GROUP BY script_id
ORDER BY scripts.name
LIMIT 0, 25

It returns:

+-----------+---------------+
| script_id | name          |
+-----------+---------------+
|         1 | jQuery        |
|         9 | jQuery Mobile |
+-----------+---------------+

If I change OR to AND, it won’t return anything at all or if I remove the brackets from the tags ( and ), it won’t return anything too.

How do I make the query constrain the tags?

Answer 1

Give this a try:

select s.script_id, s.name from scripts s
join tagged tj on s.script_id = tj.script_id
join tags t on t.tag_id = tj.tag_id
where s.name like 'jQuery%' and t.url_name in ('javascript', 'library')
group by s.script_id, s.name
having count(*) = 2
order by s.name
limit 25

The only consideration with this is that the 2 must be replaced with the amount of elements in the in clause.

Here is the fiddle.