偶遇Oracle中SQL语句中的"(+)"

之前居然从来没见到过此类写法，诸如 

select * from t_spolicy d,V_POLICYEMPLOYEE g where d.policyno = g.policyno(+)

查阅相关资料才发现此法就是外联的另外一种表现形式其等同于

select * from t_spolicy d left join V_POLICYEMPLOYEE g on d.policyno = g.policyno，

同理 select * from t_spolicy d,V_POLICYEMPLOYEE g where d.policyno(+) = g.policyno，

就等同于select * from t_spolicy d right join V_POLICYEMPLOYEE g on d.policyno = g.policyno