SELECT * FROM a full outer join b ON a.xx=b.xx--#1.a和b先产生一个结果集 inner join C on a.xx=c.xx and b.xx=c.xx--#2.上面的结果集看成一个表,再和C表INNSER JOIN
[解决办法] it depends, ms database engine could do some tunnings, it may not follow the t-sql table order. You can check sql server excution plan. [解决办法] 连接是很费资源的 [解决办法]