在第二个表上具有过滤条件的Oracle外连接 [英] Oracle outer join with filter condition on the second table

问题描述

是否有条件使结果集与以下两个语句不同?

Is there any condition under which the result sets will be different from the following two statements?

select  * from a,b where a.id = b.id and b.name = 'XYZ'
select  * from a,b where a.id =b.id(+) and b.name = 'XYZ'

我认为在这两种情况下，它都会从b.name = 'XYZ'的a和b处引入公共行.所以a.id = b.id(+)没有任何意义.

I think in both cases it will bring the common rows from a and b where b.name = 'XYZ'. So a.id = b.id(+) has no meaning.

推荐答案

否，没有条件下结果集会有所不同.

No, there is no condition under which the result sets will be different.

但是您的假设"a.id = b.id(+)没有意义"不是100％正确的.它具有含义，因为它定义了连接，否则将是a和b的笛卡尔积，其中所有行都来自a和b.name='XYZ'.

But your assumption "a.id = b.id(+) has no meaning" is not 100% correct. It has a meaning, because it defines the join, otherwise this would be a cartesian product of a and b with all rows from a and b.name = 'XYZ'.

(+)无效，因为该语句在语义上"是错误的.在id上进行外部联接在名称上进行联接是没有意义的.

What has no effect is the (+), because the statement is "semantically" wrong. It makes no sense to outer join on id but to join on name.

通常需要这样的东西:

select  * from a,b where a.id =b.id(+) and b.name(+) = 'XYZ';

在 http://www.sqlfiddle.com/#!4/d19b4上的简短示例/15

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