Oracle-查询-多表连接查询

• 左外连接是以join左边作为主表，右连接以join右边做为主表
• 外连接查询出来的结果相当于两个部分，一个部分是交集部分（相当于利用等值活非等值连接查询出来的结果），另外一个部分是连接条件主表中有而从表中没有的部分（这一部分显示的连接条件为null，这一部分是等值活非等值连接不能满足的）

sql92

等值连接

SELECT e.last_name,d.department_name,l.city
FROM employees e,departments d,locations l
WHERE e.department_id = d.department_id AND d.location_id = l.location_id

非等值连接

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 FOR UPDATE;

自链接

SELECT e.employee_id,e.last_name,m.employee_id,m.last_name
FROM employees e,employees m
WHERE e.manager_id = m.employee_id;

左连接

SELECT last_name,e.department_id,department_name
FROM employees e,departments d
WHERE e.department_id = d.department_id(+)

右外连接

SELECT last_name,e.department_id,department_name
FROM employees e,departments d
WHERE e.department_id(+) = d.department_id

 

sql99

内连接

与等值连接结果相同

SELECT e.last_name,d.department_name
FROM employees e 
INNER JOIN departments d ON e.department_id = d.department_id
--
SELECT e.last_name,d.department_name
FROM employees e 
JOIN departments d ON e.department_id = d.department_id

SELECT e.last_name,d.department_name,l.city
FROM employees e 
JOIN departments d ON e.department_id = d.department_id
JOIN locations l ON d.location_id = l.location_id
-- 等价于
SELECT e.last_name,d.department_name,l.city
FROM employees e,departments d,locations l
WHERE e.department_id = d.department_id AND d.location_id = l.location_id

左外连接

SELECT e.employee_id,e.last_name,d.department_name
FROM employees e 
LEFT OUTER JOIN departments d ON e.department_id = d.department_id
LEFT OUTER JOIN job_grades j ON e.salary BETWEEN j.lowest_sal AND j.highest_sal
WHERE d.department_name LIKE '%S%';

右外连接

SELECT e.employee_id,e.last_name,d.department_name
FROM employees e 
RIGHT OUTER JOIN departments d ON e.department_id = d.department_id;

全外连接

SELECT e.employee_id,e.last_name,d.department_name
FROM employees e 
FULL OUTER JOIN departments d ON e.department_id = d.department_id;

 

练习

-- 查询出 last_name 为 'Chen' 的 manager 的信息. (员工的 manager_id 是某员工的 employee_id) 
SELECT e.employee_id, e.email,m.last_name
FROM employees e,employees m
WHERE e.department_id = m.employee_id AND e.last_name = 'Chen';
-- 子查询
SELECT m.employee_id,m.last_name
FROM employees m
WHERE m.employee_id = (
                        SELECT e.employee_id
                        FROM employees e
                        WHERE e.last_name = 'Chen'
                    );

-- 左外连接
select last_name, e.department_id, department_name
from employees e, departments d
where e.department_id = d.department_id(+)
-- 右外连接
select last_name, d.department_id, department_name
from employees e, departments d
where e.department_id(+) = d.department_id

-- 1.	显示所有员工的姓名，部门号和部门名称。
SELECT e.last_name,d.department_id,d.department_name
FROM employees e 
JOIN departments d
ON e.department_id = d.department_id
--
SELECT e.last_name,department_id,d.department_name
FROM employees e 
JOIN departments d USING(department_id);

-- 2.	查询90号部门员工的job_id和90号部门的location_id
SELECT DISTINCT e.job_id,d.location_id
FROM employees e
JOIN departments d
ON e.department_id = d.department_id
WHERE d.department_id = '90';

-- 3.	选择所有有奖金的员工的 last_name , department_name , location_id , city
SELECT e.last_name,d.department_name,l.location_id,l.city
FROM employees e
JOIN departments d
ON e.department_id = d.department_id
JOIN locations l
ON d.location_id = l.location_id
WHERE e.commission_pct IS NOT NULL;

-- 4.	选择city在Toronto工作的员工的 last_name , job_id , department_id , department_name
SELECT e.last_name,e.job_id,d.department_id,d.department_name
FROM employees e
JOIN departments d
ON e.department_id = d.department_id
JOIN locations l
ON d.location_id = l.location_id
WHERE l.city = 'Toronto';