mysql - 如何根据mysql中的条件更改连接类型？

Question

我正在尝试做这样的事情:

SELECT m.id, u.first_name AS otherUser
FROM matches AS m
IF (u.id=m.user2ID)
    Inner JOIN users AS u ON u.id = m.user1ID
ELSE
    LEFT JOIN users AS u ON u.id = m.user2ID
ENDIF
WHERE m.user1ID=2 OR m.user2ID=2

现在我打算根据条件更改连接类型。我可以这样做吗？如果是那么怎么办？

更新:-我在这里想要实现的是，当特定条件为真时更改连接类型，例如:

if(a==1){
  Then do inner join
}else{
 Then do left join
}

Answer 1

如果这可能是等价的

SELECT m.id, u.first_name AS otherUser
FROM matches AS m
LEFT JOIN users  as u  
   ON ( (u.id=m.user2ID AND ON u.id = m.user1ID ) OR u.id = m.user2ID )
WHERE m.user1ID=2 OR m.user2ID=2