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

问题描述

在我们正在迁移的基于 Oracle 的应用程序中发现以下内容(通用):

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 子句中有什么作用?我以前从未见过这样使用它.

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

推荐答案

根据="的哪一侧，(+) 在，它表示 LEFT OUTER 或 RIGHT OUTER 连接(在这种情况下，它是左外连接)这是旧的 Oracle 语法，有时会被最先学习它的人更喜欢，因为他们喜欢这样可以缩短他们的代码.

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.

为了可读性，最好不要使用它.

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

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