什么时候或为什么你会使用右外连接而不是左？ [英] When or why would you use a right outer join instead of left?

问题描述

维基百科说明：

在实践中，很少使用显式的右外连接，因为它们总是可以用左外连接替换，不提供其他功能。

"In practice, explicit right outer joins are rarely used, since they can always be replaced with left outer joins and provide no additional functionality."

提供他们喜欢使用RIGHT符号的情况，为什么？
我不能想到一个理由来使用它。对我来说，它不会使事情更清楚。

Can anyone provide a situation where they have preferred to use the RIGHT notation, and why? I can't think of a reason to ever use it. To me, it wouldn't ever make things more clear.

编辑：
我是一个Oracle老将，使新年的决议从（+）语法。我想做正确

I'm an Oracle veteran making the New Year's Resolution to wean myself from the (+) syntax. I want to do it right

推荐答案

我可以想到使用RIGHT OUTER JOIN的唯一原因是试图让你的SQL更多的自我记录。

The only reason I can think of to use RIGHT OUTER JOIN is to try to make your SQL more self-documenting.

对于在一对多关系的从属（多）侧有空行的查询，你可能想使用左连接

You might possibly want to use left joins for queries that have null rows in the dependent (many) side of one-to-many relationships and right joins on those queries that generate null rows in the independent side.

这也可以在生成的代码中出现，或者如果商店的编码需求指定了在FROM子句。

This can also occur in generated code or if a shop's coding requirements specify the order of declaration of tables in the FROM clause.

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