使用 SQL 打印来自两个不同 table 的数据，但使用第三个 table 作为两者之间的 link

Question

我有 3 个 Table。员工、地点和部门。

我需要写一个 SQL 语句来显示来自 EMPLOYEES 的 first_name 和他们居住的城市。

链接的方式是这样的：

每个员工都有一个 Employee_ID，可以在 EMPLOYEES table 和 DEPARTMENTS table
中找到
DEPARTMENTS table 有一个 Location_ID 也存在于 LOCATIONS Table.

我会添加图片来更好地解释它，但我不知道该声明应该是什么样子。提前致谢。

Answer 1

您可以加入：

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

Answer 2

你都说了，只是加入那些表。先采样数据；您需要的查询从第 18 行开始。

SQL> with
  2  employees (first_name, employee_id) as
  3    (select 'Jack', 1 from dual union all
  4     select 'Jill', 2 from dual union all
  5     select 'Paul', 3 from dual
  6    ),
  7  departments (employee_id, location_id) as
  8    (select 1, 10 from dual union all
  9     select 2, 20 from dual union all
 10     select 3, 30 from dual
 11    ),
 12  locations (location_id, city) as
 13    (select 10, 'Narnia'   from dual union all
 14     select 20, 'Valhalla' from dual union all
 15     select 30, 'Atlantis' from dual
 16    )
 17  --
 18  select e.first_name, l.city
 19  from employees e join departments d on e.employee_id = d.employee_id
 20  join locations l on l.location_id = d.location_id
 21  order by e.employee_id;

FIRS CITY
---- --------
Jack Narnia
Jill Valhalla
Paul Atlantis

SQL>

使用 SQL 打印来自两个不同 table 的数据，但使用第三个 table 作为两者之间的 link

Using SQL to print data from two different tables but using a third table as a link between the two

sql

oracle

inner-join

oracle-sqldeveloper