oracle的SQL语句中的(+)是干什么用的？

Question

oracle的SQL语句中的(+)是干什么用的？

Answer 1

oracle特有的左外联书写方式，当然你也可以用传统的通用的左外联，比如给你举个例子SELECT s.name AS 姓名,g.grade AS 分数,c.cid AS 课程名FROM tbl_student s LEFT OUTER JOIN tbl_grade g ON s.StudentId=g.sid LEFT OUTER JOIN tbl_class c ON g.cid=c.ClassId它跟下面等价SELECT s.name AS 姓名,g.grade AS 分数,c.classname AS 课程名FROM tbl_student s,tbl_grade g,tbl_class cWHERE (s.StudentId=g.sid(+)) AND (g.cid=c.ClassId(+))