Oracle:在WHERE子句中`(+)`有什么作用? [英] Oracle: What does `(+)` do in a WHERE clause?

问题描述

在我们正在迁移(通用) 的基于Oracle的应用程序中找到以下内容:

Found the following in an Oracle-based application that we're migrating (generalized):

SELECT
    Table1.Category1,
    Table1.Category2,
    count(*) as Total,
    count(Tab2.Stat) AS Stat
FROM Table1, Table2
WHERE (Table1.PrimaryKey = Table2.ForeignKey(+))
GROUP BY Table1.Category1, Table1.Category2

(+)在WHERE子句中做什么?我以前从未见过像这样使用过.

What does (+) do in a WHERE clause? I've never seen it used like that before.

推荐答案

取决于(=)在"="的哪一侧，它表示向左或向右连接(在这种情况下，它是左外连接).这是旧的Oracle语法，有时它是那些首先学习它的人所喜欢的，因为他们喜欢这样做，从而使代码更短.

Depending on which side of the "=" the "(+) is on, it denotes a LEFT OUTER or a RIGHT OUTER join (in this case, it's a left outer join). It's old Oracle syntax that is sometimes preferred by people who learned it first, since they like that it makes their code shorter.

出于可读性考虑，最好不要使用它.

Best not to use it though, for readability's sake.

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