Mam 3 tabele: users, messages, books
Zapytanie:

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SELECT COUNT(m.message_id), u.user_nick
FROM messages m, users u
WHERE m.message_user_id = u.user_id AND u.user_id = 1 LIMIT 1
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No i zwraca mi poprawnie!

Drugie zapytanie jest prawie identyczne:

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SELECT COUNT(b.book_id), u.user_nick
FROM books b, users u
WHERE b.book_user_id = u.user_id AND u.user_id = 1 LIMIT 1
[SQL] pobierz, plaintext 

Zas zapytanie:

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SELECT COUNT(b.book_id), COUNT(m.message_id), u.user_nick
FROM books b, messages m, users u
WHERE u.user_id = 1 b.book_user_id = u.user_id AND m.message_user_id = u.user_id LIMIT 1
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Zwraca dwie takie same liczby b.book_id i m.message_id

Jak zrobic to w jednym zapytaniu, aby wynik wygladal tak mniejwiecej:

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SELECT COUNT(b.book_id), COUNT(m.message_id), u.user_nick
FROM books b INNER JOIN users u ON(b.book_user_id = u.user_id) INNER JOIN messages m ON(m.message_user_id = u.user_id)
WHERE u.user_id = 1
GROUP BY u.user_nick
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A powinno byc:
3
5
kicaj_

[UPDATE]
Szczegolowo przeszukalem forum i znalazlem, po lekkiej modyfikacji:

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SELECT u.user_nick, COUNT( DISTINCT b.book_id ) AS books, COUNT( DISTINCT m.message_id ) AS messages
FROM users u
LEFT JOIN books b ON ( u.user_id = b.book_user_id ) 
LEFT JOIN messages m ON ( u.user_id = m.message_user_id ) 
WHERE u.user_id =2
GROUP BY u.user_id
[SQL] pobierz, plaintext