Prova så här, jag har inget schema för att testa det själv men jag känner att det borde fungera (eller något sånt här)
SELECT * FROM questions, connections
LEFT JOIN answers ON (questions.id = answers.id AND
connections.username2 = answers.username)
where connections.username1 = 'mikha';
så småningom så här
SELECT * FROM questions
LEFT JOIN answers ON (questions.id = answers.id)
LEFT JOIN connections ON (connections.username2 = answers.username)
where connections.username1 = 'mikha';
EDIT:Jag hittade detta i dokumentationen
Så för ditt fall kan det vara
SELECT * FROM questions
LEFT JOIN connections
LEFT JOIN answers ON (connections.username1 = 'mikha' AND questions.id = answers.id AND
connections.username2 = answers.username)