oracle视图总结（创建、查询、修改、删除等）

标签：oracle   视图   view   

视图定义：

— —视图是一种虚表。

为什么使用视图？

— —控制数据访问
— —简化查询
— —避免重复访问相同的数据

创建视图：在 CREATE VIEW 语句中嵌入子查询，子查询可以是复杂的 SELECT 语句

<span style="font-size:14px;">create or replace view empview 
as 
select employee_id emp_id,last_name name,department_name
from employees e,departments d
Where e.department_id = d.department_id</span>

<span style="font-size:14px;">CREATE VIEW  salvu50
AS 
SELECT  employee_id  ID_NUMBER, 
            last_name    NAME,
            salary*12    ANN_SALARY
FROM    employees
WHERE   department_id = 50;
View created.</span>

查询视图：SELECT  *  FROM    salvu50;

修改视图：使用CREATE OR REPLACE VIEW 子句修改视图

<span style="font-size:14px;">CREATE OR REPLACE VIEW empvu80
  (id_number, name, sal, department_id)
AS SELECT  employee_id, first_name || ' ' || last_name, 
           salary, department_id
   FROM    employees
   WHERE   department_id = 80;
View created.</span>

<span style="font-size:14px;">CREATE VIEW	dept_sum_vu
  (name, minsal, maxsal, avgsal)
AS SELECT	 d.department_name, MIN(e.salary), 
             MAX(e.salary),AVG(e.salary)
   FROM      employees e, departments d
   WHERE     e.department_id = d.department_id 
   GROUP BY  d.department_name;
View created.</span>

可以在简单视图中执行 DML 操作
当视图定义中包含以下元素之一时不能使用delete:
— —组函数
— —GROUP BY 子句
— —DISTINCT 关键字
— —ROWNUM 伪列

<span style="font-size:14px;">create or replace view sal_view
as select
avg(salary) avg_sal from employees
group by department_id
</span>

当视图定义中包含以下元素之一时不能使insert:
— —组函数
— —GROUP BY 子句
— —DISTINCT 关键字
— —ROWNUM 伪列
— —列的定义为表达式
— —表中非空的列在视图定义中未包括

屏蔽 DML 操作：

可以使用 WITH READ ONLY 选项屏蔽对视图的DML 操作
任何 DML 操作都会返回一个Oracle server 错误

<span style="font-size:14px;">CREATE OR REPLACE VIEW empvu10
    (employee_number, employee_name, job_title)
AS SELECT	employee_id, last_name, job_id
   FROM     employees
   WHERE    department_id = 10
   WITH READ ONLY;
View created.</span>

<span style="font-size:14px;">DROP VIEW empvu80;
View dropped.</span>

查询最大的几个值的 Top-N 分析:

<span style="font-size:14px;">SELECT [column_list], ROWNUM  
FROM   (SELECT [column_list] 
        FROM table
        ORDER  BY Top-N_column)
WHERE  ROWNUM <=  N;</span>

<span style="font-size:14px;">select *
from(
select rownum rn,employee_id,salary
from(
select employee_id,salary,last_name
from employees
order by salary desc
)
)where rn <=50 and rn >40</span>

oracle视图总结（创建、查询、修改、删除等）

标签：oracle   视图   view   

原文地址：http://blog.csdn.net/yuzongtao/article/details/40601993