MySQL / PHP: Find similar / related items by tag / taxonomy

Question

I have a cities table which looks like this.

|id| Name    |
|1 | Paris   |
|2 | London  |
|3 | New York|

I have a tags table which looks li

Answer 1

Could this be a push in the right direction?

SELECT cities.name, ( 
                    SELECT cities.id FROM cities
                    JOIN cities_tags ON cities.id=cities_tags.city_id
                    WHERE tags.id IN(
                                     SELECT cities_tags.tag_id
                                     FROM cites_tags
                                     WHERE cities_tags.city_id=cites.id
                                     )
                    GROUP BY cities.id
                    HAVING count(*) > 0
                    ) as matchCount 
FROM cities
HAVING matchCount >0

What I tried was this:

// Find the citynames:
Get city.names (SUBQUERY) as matchCount FROM cities WHERE matchCount >0

// the subquery:
select the amount of tags cities have which (SUBSUBQUERY) also has

// the subsubquery
select the id of the tags the original name has