问题 左连接更快或内连接更快？

那么......哪一个更快（NULl值不是问题），并被索引。

SELECT * FROM A
  JOIN B b ON b.id = a.id
  JOIN C c ON c.id = b.id 
 WHERE A.id = '12345'

使用左连接：

SELECT * FROM A
 LEFT JOIN B ON B.id=A.bid
 LEFT JOIN C ON C.id=B.cid
WHERE A.id = '12345'

这是实际的查询 这是......两者都返回相同的结果

Query (0.2693sec) :
    EXPLAIN EXTENDED SELECT * 
    FROM friend_events, zcms_users, user_events, 
    EVENTS WHERE friend_events.userid = '13006'
    AND friend_events.state =0
    AND UNIX_TIMESTAMP( friend_events.t ) >=1258923485
    AND friend_events.xid = user_events.id
    AND user_events.eid = events.eid
    AND events.active =1
    AND zcms_users.id = user_events.userid

EXPLAIN

    id select_type table type possible_keys key key_len ref rows Extra 
    1 SIMPLE zcms_users ALL PRIMARY NULL NULL NULL 43082 
    1 SIMPLE user_events ref PRIMARY,eid,userid userid 4 zcms_users.id 1 
    1 SIMPLE events eq_ref PRIMARY,active PRIMARY4 user_events.eid 1 Using where
    1 SIMPLE friend_events eq_ref PRIMARY PRIMARY 8 user_events.id,const 1 Using where



    LEFTJOIN QUERY: (0.0393 sec)

    EXPLAIN EXTENDED SELECT * 
    FROM `friend_events` 
    LEFT JOIN `user_events` ON user_events.id = friend_events.xid
    LEFT JOIN `events` ON user_events.eid = events.eid
    LEFT JOIN `zcms_users` ON user_events.userid = zcms_users.id
    WHERE (
    events.active =1
    )
    AND (
    friend_events.userid = '13006'
    )
    AND (
    friend_events.state =0
    )
    AND (
    UNIX_TIMESTAMP( friend_events.t ) >=1258923485
    )


EXPLAIN
    id select_type table type possible_keys key key_len ref rows Extra 
    1 SIMPLE friend_events ALL PRIMARY NULL NULL NULL 53113 Using where
    1 SIMPLE user_events eq_ref PRIMARY,eid PRIMARY 4 friend_events.xid 1 Using where
    1 SIMPLE zcms_users eq_ref PRIMARY PRIMARY 4 user_events.userid 1 
    1 SIMPLE events eq_ref PRIMARY,active PRIMARY 4 user_events.eid 1 Using where