(+)运算符在PL/SQL的where子句中意味着什么？

Question

我有一个SQL查询类似于: -

Select Table1.attr1, Table1.attr2, Table2.attr3, Table2.attr4
From Tab1 Tabel1, Tab2 Tabel2
Where Tabel1.Attr = Tabel2.Attr (+)

那么上面是什么意思呢？这是一个正确的外部联接吗？

Answer 1

是的,这意味着正确加入.如果语句类似......其中Tabel1.Attr(+)= Tabel2.Attr,则必须保持连接.

Answer 2

我认为这是一个左外连接（尽管当前批准的答案说它是一个右外连接）。来自Oracle 文档：

Using Outer Joins: Examples

SELECT d.department_id, e.last_name
   FROM departments d LEFT OUTER JOIN employees e
   ON d.department_id = e.department_id
   ORDER BY d.department_id;


Users familiar with the traditional Oracle Database outer
joins syntax will recognize the same query in this form:

SELECT d.department_id, e.last_name
   FROM departments d, employees e
   WHERE d.department_id = e.department_id (+)
   ORDER BY d.department_id;

对于 RIGHT OUTER JOIN，您可以在 = 符号之前放置 (+) 符号，例如。

SELECT d.department_id, e.last_name
   FROM departments d, employees e
   WHERE d.department_id (+) = e.department_id
   ORDER BY d.department_id;