ORACLE 第4节 多表查询

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学习目标：

Oracle连接

等值连接：

使用连接在多个表中查询数据。

SELECT  table1.column, table2.column

FROM  table1, table2

WHERE  table1.column1= table2.column2;

select e.employee_id,e.last_name,d.department_id
from employees e,departments d
where e.department_id = d.department_id

select e.employee_id,e.last_name,d.department_id,l.city
from employees e,departments d,locations l
where e.department_id = d.department_id and
d.location_id = l.location_id

select e.last_name,e.salary,j.grade_level
from employees e,job_grades j
where e.salary between j.lowest_sal and j.highest_sal

--左外连接

select e.employee_id,e.last_name,d.department_name
from employees e,departments d
where e.department_id = d.department_id(+)

--右外连接

select e.employee_id,e.last_name,d.department_name
from employees e,departments d
where e.department_id(+) = d.department_id

select e.employee_id,e.last_name,d.department_name
from employees e natural join departments d

使用 USING子句创建连接:

JOIN和USING子句经常同时使用。

select e.employee_id,e.last_name,d.department_name
from employees e join departments d
using(department_id)

这种方法有局限性：如果两个表中的列名（一个叫department_id,另外一个叫id）不一样，这个方法就失效了。

使用ON子句创建连接（常用）:

<pre name="code" class="sql">select e.employee_id,e.last_name,d.department_name
from employees e 
join departments d
on e.department_id = d.department_id

select e.employee_id,e.last_name,d.department_name,l.city
from employees e 
<strong>join departments d</strong>
on e.department_id = d.department_id
<strong>join locations l</strong>
on d.location_id = l.location_id

ORACLE 第4节 多表查询

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原文地址：http://blog.csdn.net/u014338577/article/details/47687605