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      oracle sql中join关键字和inner join关键字有什么区别?

      时间:2023-10-09

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              • 本文介绍了oracle sql中join关键字和inner join关键字有什么区别?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着跟版网的小编来一起学习吧!

                问题描述

                我找不到关于关键字 join 的文档,但我在网上看到了使用它的示例.

                I can't find documentations on the key word join but I saw examples on the web using it.

                我在 Oracle hr 模式中做了一些实验,我有表 departments:

                I was doing some experiment with it in Oracle hr schema, where I have table departments:

                • deparment_name
                • manager_id
                • location_id

                employees:

                • first_name
                • employee_id

                和表locations:

                • location_id
                • city

                查询应返回部门名称,部门经理的名字,部门所在城市.

                Query should return the department_name, first_name of the manager of the department, and the city where the department is located.

                与使用关键字inner join

                带有join的代码:

                select d.department_name, e.first_name,l.city
                from departments d
                   join employees e on d.manager_id=e.employee_id
                   join locations l on d.location_id=l.location_id
                

                带有内连接的代码:

                select d.department_name, e.first_name,l.city
                from departments d
                   inner join employees e on d.manager_id=e.employee_id
                   inner join locations l on d.location_id=l.location_id
                

                这两种情况是否有区别,或者我只是偶然发现它们返回相同结果的情况?

                Is there a difference between the two condition, or am I just happen to stumble on a situation where they return the same results?

                推荐答案

                • 遵循 1992 ANSI SQL 参考,INNER 是可选的:
                • 查询表达式 179 7.5 - 连接表

                  Query expressions 179 7.5 - joined table

                  3) 如果指定了合格的联接联接类型未指定指定,则 INNER 是隐式的.

                  3) If a qualified join is specified and a join type is not specified, then INNER is implicit.

                  • 遵循 Oracle 标准(9i 以后),INNER 前缀也是可选的.在 9i 之前,Oracle 不遵循 ANSI 规则,甚至不支持 JOIN 语法.
                    • Following Oracle Standards (9i onward), the INNER prefix is also optional. Before 9i, Oracle didn't follow ANSI rules, and didn't even support JOIN syntax.
                    • 这篇关于oracle sql中join关键字和inner join关键字有什么区别?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持跟版网!

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