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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 c WHERE (s.StudentId=g.sid(+)) AND (g.cid=c.ClassId(+))
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原文地址：http://www.cnblogs.com/xiao-fy/p/5171333.html
