ON JOIN

Ahoj mam problemy se slozitejsimy SQL dotazy

napr.
mam tri tabulky forums, projects, messages
na forums je napojene messages, forums.forum_id = messages.message_id

vypisu si forums a project a pritom si vypisu pocet message, ve foru

Select f.forum_id, p.project_id count(m.message_id)
FROM forums as f, projects as p
left join messages as m on
m.message_forum=f.forum_id
where f.forum_id = p.project_id
group by f.forum_id

coz nahlasi #1054 - Unknown column 'f.forum_id' in 'on clause'

pritom modifikace
Select f.forum_id, p.project_id count(m.message_id)
FROM forums as f
left join messages as m on
m.message_forum=f.forum_id
group by f.forum_id

funguje
a funguje i modifikace

Select f.forum_id, p.project_id count(m.message_id)
FROM forums as f, projects as p
left join messages as m on
m.message_forum=1
where f.forum_id = p.project_id
group by f.forum_id

ale samorejmne ne z vysledkem ktery bych chtel

trochu slozitejsi dotazy sem tu mel pred par lety a ted koukam ze nejedou.

Tento problem znam, na nejake verzi MySQL to projde a na nektere ne.
Ja Ti reknu, v cem je rozdil - v prvnim priklade mas FROM dva tabulky a v dalsich dvou jenom jednu. Kdyz mas tri tabulky, pouzijes 3x LEFT JOIN pres indexy, pak by to melo projit ;)
Zkratka kolik mas tabulek, tolik musis mit JOINu.

Viz muj priklad:
SELECT COUNT(".$this->table_gb.".Id) AS comments,".$this->table_users.".Id AS userid,".$this->table_news.".Id,".$this->table_news.".Type,".$this->table_news.".Date,Nick,Header FROM ".$this->table_news." LEFT JOIN ".$this->table_users." ON (".$this->table_news.".Id_user=".$this->table_users.".Id) LEFT JOIN ".$this->table_gb." ON (".$this->table_gb.".Id_parent=".$this->table_news.".Id) AND (".$this->table_gb.".Type=0) WHERE (".$this->table_news.".Type=$typ) GROUP BY ".$this->table_news.".Id ORDER BY ".$this->table_news.".Date DESC