Oracle MATERIALIZED VIEW -- 物化视图

1，ORACLE：materialized view和普通VIEW有什么区别
   materialized view(MV)是自动刷新或者手动刷新的，View不用刷新 MV也可以直接update，但是不影响base table，对View的update反映到base table上 MV主要用于远程数据访问，mv中的数据需要占用磁盘空间，view中不保存数据。

2，权限
   必须具有 RESOURCE 权限和实现化视图 (Materialized View) 定义中的表的 SELECT 权限。要为其他用户创建实现化视图 (Materialized View)，还必须具有 DBA 权限。

3，创建物化视图
   CREATE MATERIALIZED VIEW MV_ADDRESS
   nologging
   REFRESH COMPLETE AS 
   SELECT
   trim(ID) as ID
   ,trim(COUNTRY) as COUNTRY
   ,trim(PROV) as PROV
   ,trim(CITY) as CITY
   ,trim(TOWN) as TOWN
   FROM 
   ADDRESS@oracle_dlk;

   COMMENT ON MATERIALIZED VIEW MV_ADDRESS IS '住所表';
   COMMENT ON COLUMN MV_ADDRESS.ID IS 'ID';
   COMMENT ON COLUMN MV_ADDRESS.COUNTRY IS '国家';
   COMMENT ON COLUMN MV_ADDRESS.PROV IS '省份';
   COMMENT ON COLUMN MV_ADDRESS.CITY IS '城市';
   COMMENT ON COLUMN MV_ADDRESS.TOWN IS '城镇';

4，SQL刷新物化视图