Oracle 的视图
源数据：
-- Create table
create table STU_INFO
(id NUMBER not null,name VARCHAR2(8),score NUMBER(4,1),class VARCHAR2(2)
)
tablespace STUDENTpctfree 10initrans 1maxtrans 255storage(initial 64Knext 1Mminextents 1maxextents unlimited);
-- Create/Recreate primary, unique and foreign key constraints
alter table STU_INFOadd primary key (ID)using index tablespace STUDENTpctfree 10initrans 2maxtrans 255storage(initial 64Knext 1Mminextents 1maxextents unlimited);
1. 创建普通视图
CREATE [OR REPLACE] VIEW view_name [(column1, column2, ...)]
AS
SELECT column1, column2, ...
FROM table1, table2, ...
WHERE condition;
CREATE OR REPLACE VIEW STU_INFO_VIEW AS
SELECT STU_INFO.ID,STU_INFO.NAME,STU_INFO.SCORE
FROM STU_INFO WHERE STU_INFO.SCORE>60;
ps: 所有的视图的是基于基表的数据,相当于引用那个表的数据,当普通视图的值发生改变时,则基表值也会改变,反之亦然。
优点： 实时性，简化查询，安全性。 缺点： 影响性能，数据一致性（底层数据发生改变视图数据也会改变）
2. 创建物化视图
CREATE [MATERIALIZED] VIEW view_name
[REFRESH {FAST|COMPLETE|FORCE ON | COMMIT | DEMAND}] -- 刷新方式 增量刷新 完全刷新 自动选择|自动刷新 手动刷新 默认： FORCE ON COMMIT
[START WITH date_value]
[NEXT date_value]
[WITH {PRIMARY KEY|ROWID}]
[ENABLE|DISABLE] QUERY REWRITE
AS
select_statement;
CREATE MATERIALIZED VIEW MV_STU_INFO
REFRESH FORCE ON DEMAND
AS
SELECT STU_INFO.ID,STU_INFO.NAME,STU_INFO.SCORE
FROM STU_INFO;
BEGINDBMS_MVIEW.REFRESH('MV_STU_INFO', 'C');
END;
-- 执行手动刷新
ps：优点：性能提升，数据一致性，分布式数据处理。 缺点： 占用存储空间，数据更新延迟
3. 创建物化增量视图
-- 前提是必须创建物化视图日志，记录基表发生了哪些变化（增删改查），用这些记录去更新物化视图
CREATE MATERIALIZED VIEW LOG ON "TABLE_NAME" WITH <PRIMARY KEY | ROWID>CREATE MATERIALIZED VIEW LOG ON STU_INFO WITH ID;
CREATE MATERIALIZED VIEW MV_STU_INFO_FAST
REFRESH FAST
AS
SELECT ID,NAME FROM STU_INFO;
3. oracle查询表结构
SELECT COLUMN_NAME, DATA_TYPE, DATA_LENGTH, NULLABLE
FROM ALL_TAB_COLUMNS
WHERE TABLE_NAME = 'STU_INFO'; -- 替换为实际的表名
