Oracle 多表查詢

等值和不等值連線查詢

為了避免笛卡爾集，可以在 where 加入有效的連線條件。

oracle 連線多表查詢

select table1.column, table2.column from table1, table2

where table1.column1 = table2.column2;

等值連線

select employees.employee_id, employees.last_name, employees.department_id, departments.department_id, departments.location_id from employees, departments

where employees.department_id = departments.department_id;

連線 n個表,至少需要 n-1個連線條件。例如：連線三個表，至少需要兩個連線條件。

-- 練習：查詢出公司員工的 last_name, department_name, city select last_name, department_name, city from employees e ,departments d ,locations l

where e.department_id = d.department_id and d.location_id = l.location_id

非等值連線

-- employees表中的列工資應在job_grades表中的最高工資與最低工資之間 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;

內連線、外連線(左（或右）外連線、滿外連線)

內連線

select e.last_name, d.department_name from employees e, departments d

where e.department_id = d.department_id

-- sql1999語法的方式 select e.last_name, d.department_name from employees e

inner join departments d on e.department_id = d.department_id

外連語法

select  table1.column, table2.column
from  table1, table2
where table1.column(+) = table2.column;
-- 示例
select e.last_name, d.department_name 
from employees e, departments d
where e.department_id(+) = d.department_id
-- sql1999方式
select e.last_name, d.department_name 
from employees e right outer join departments d
on (e.department_id = d.department_id)

select  table1.column, table2.column
from  table1, table2
where table1.column = table2.column(+);
-- 示例
select e.last_name, d.department_name 
from employees e, departments d
where e.department_id = d.department_id(+)
-- sql1999方式
select e.last_name, d.department_name 
from employees e left outer join departments d
on (e.department_id = d.department_id)

滿外連線

-- 滿外連線 select e.last_name, e.department_id, d.department_name from employees e full outer join departments d

on (e.department_id = d.department_id)

自連線

-- 練習：查詢出 last_name 為 『chen』 的員工的 manager 的資訊
select worker.last_name || ' works for ' || manager.last_name
from employees worker , employees manager
where worker.manager_id = manager.employee_id  and initcap(worker.last_name) = 'chen'

叉集(了解)

select last_name, department_name from employees

cross join departments

自然連線

返回的是，兩個表中具有相同名字的列的「且、交集」，而非「或，並集」。即：比如employee類和department類都有

department_id和manager_id，返回二者都相同的結果。

select department_id, department_name, location_id, city from departments

natural join locations

使用using建立連線

select  last_name,department_name 
from employees 
join departments using (department_id);

使用on 子句建立連線 (常用)

select e.employee_id, e.last_name, e.department_id, d.department_id, d.location_id from employees e join departments d on (e.department_id = d.department_id) -- 使用on 建立多表連線 select employee_id, city, department_name from employees e join departments d on d.department_id = e.department_id join locations l

on d.location_id = l.location_id

Oracle 多表查詢

Oracle 多表查詢

Oracle 多表查詢

oracle 多表查詢

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