多表JOIN优化问题
SELECT u.* FROM user u
LEFT JOIN user_data ud ON (u.user_id = ud.user_id)
LEFT JOIN account a1 ON (u.user_id = a1.user_id AND a1.acc_sx = 1)
LEFT JOIN account a2 ON (u.user_id = a2.user_id AND a2.acc_sx = 2)
WHERE u.user_id=9;
请问这条SQL,如何优化?谢谢。