修改表的内容-RETURNING/DEFAULT/MERGE/时间查询闪回/系统变更号查询闪回

returning子句：返回使用聚合函数计算的结果

VARIABLE average_product_price NUMBER

UPDATE products

SET price = price * 0.75

RETURNING AVG(price) INTO :average_product_price;

为列定义默认值：

CREATE TABLE  order_status (

order_status_id INTEGER

CONSTRAINT default_example_pk PRIMARY KEY,

status VARCHAR2(20) DEFAULT ' Order placed' NOT NULL,

last_modified DATE DEFAULT SYSDATE);

使用MERGE合并行：

MERGE INTO products p

USING product_changes pc ON (

p.product_id = pc.product_id

)

WHEN MATCHED THEN

UPDATE

SET

p.product_type_id = pc.product_type_id,

p.name = pc.name,

p.description = pc.description,

p.price = pc.price

WHEN NOT MATCHED THEN

INSERT (p.product_id,p.product_type_id,p.name,p.description,p.price)

VALUES (pc.product_id.pc.product_type_id,pc.name,pc.description,p.price);

时间查询闪回

EXECUTE DBMS_FLASHBACK.ENABLE_AT_TIME(SYSDATE - 10 / 1440)  查询显示十分钟之前的状态。

EXECUTE DBMS_FLASHBACK.DISABLE();  禁用闪回操作。

系统变更号（SCN）查询闪回

VARIABLE current_scn NUMBER

EXECUTE :current_scn := DBMS_FLASHBACK.GET_SYSTEM_CHANGE_NUMBER(); 获取当前SCN

闪回到SCN状态：

EXECUTE DBMS_FLASHBACK.ENABLE_AT_SYSTEM_CHANGE_NUMBER(:current_scn);