SQL oracle sql中join关键字和inner join关键字有什么区别？
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what is the difference between join keyword and inner join keyword in oracle sql?
提问by Cici
I can't find documentations on the key word joinbut I saw examples on the web using it.
我找不到有关该关键字的文档，join但我在网上看到了使用它的示例。
I was doing some experiment with it in Oracle hrschema, where I have table departments:
我在 Oraclehr模式中对它进行了一些实验，其中有表departments：
deparment_namemanager_idlocation_id
deparment_namemanager_idlocation_id
A table employees:
一张表employees：
first_nameemployee_id
first_nameemployee_id
And table locations:
和表locations：
location_idcity
location_idcity
Query should return the department_name, first_name of the manager of the department, and the city where the department is located.
查询应返回部门名称、部门经理的名字和部门所在的城市。
The code using the keyword joinseem to return the some result in comparison to using the keyword inner join
与使用关键字join相比，使用关键字的代码似乎返回了一些结果inner join
Code with join:
代码join：
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
Code with inner join:
代码inner join：
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
Is there a difference between the two condition, or am I just happen to stumble on a situation where they return the same results?
这两种情况有区别吗，还是我只是偶然发现它们返回相同结果的情况？
回答by Sebas
- Following 1992 ANSI SQL reference, INNER is optional:
- 遵循 1992 ANSI SQL 参考，INNER 是可选的：
Query expressions 179 7.5 - joined table
3) If a qualified joinis specified and a join typeis not specified, then INNER is implicit.
查询表达式 179 7.5 - 连接表
3) 如果指定了限定连接但未指定连接类型，则 INNER 是隐式的。
- Following Oracle Standards (9i onward), the
INNERprefix is also optional. Before 9i, Oracle didn't follow ANSI rules, and didn't even supportJOINsyntax.
- 按照 Oracle 标准（从9i 开始），
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。
