Question

我有一个SQL查询，如： -

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

那么上述意味着什么呢？这是一个正确的外部联接吗？

Answer 1

是的，这意味着正确加入。如果声明就像....其中Tabel1.Attr（+）= Tabel2.Attr，它必须保持连接。

Answer 2

你是对的，+是正确的加入

Answer 3

这是一个左外部联接。您可以在此处找到使用示例的示例：https://www.techonthenet.com/oracle/joins.php

Answer 4

我认为这是一个左外部联接（尽管批准的答案表示这是一个右外部联接）。来自Oracle documentation：

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，请将（+）号放在=号之前，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;

Answer 5

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

与可识别的语法相同：

Select Table1.attr1, Table1.attr2, Table2.attr3, Table2.attr4 From Tab1 Tabel1
LEFT OUTER JOIN Tab2 Tabel2 on Tabel1.Attr = Tabel2.Attr

（+）运算符在PL / SQL的where子句中意味着什么？

5 个答案: