多链表查询和子查询有什么区别？多链表查询和子查询有什么区别?有哪位大神能说说吗？关于SQL
http://www.cnblogs.com/ylbtech/p/3498221.html
http://www.cnblogs.com/ylbtech/p/3498221.html
以下是摘自oracle ocp9i文档：
outer join syntax:
1)you use an outer join to also see rows that do not meet the join condition
2)the outer join operator is the plus sign(+)
outer join restrictions:
1)the outer join operator can appear on only one side of the expression:the side that has information missing.it returns those rows from one table that have no direct match in the other table.
2)a condition involving an outer join cannot use the IN operator or be linked to another condition by the OR operator.
具体的话可以参考：http://www.hello-code.com/blog/oracle/201404/3324.html