oracle數據庫支持物化視圖--不是基於基表的虛表，而是根據表實際存在的實表，即物化視圖的數據存儲在非易失的存儲設備上。
下面實驗創建ON COMMIT 的FAST刷新模式，在mysql中用觸發器實現insert , update , delete 刷新操作
1、基礎表創建，Orders 表為基表，Order_mv為物化視圖表
復制代碼 代碼如下:
mysql> create table Orders(
-> order_id int not null auto_increment,
-> product_name varchar(30)not null,
-> price decimal(10,0) not null ,
-> amount smallint not null ,
-> primary key (order_id));
Query OK, 0 rows affected
mysql> create table Order_mv(
-> product_name varchar(30) not null,
-> price_sum decimal(8.2) not null,
-> amount_sum int not null,
-> price_avg float not null,
-> order_cnt int not null,
-> unique index(product_name));
Query OK, 0 rows affected
2、insert觸發器
復制代碼 代碼如下:
delimiter $$
create trigger tgr_Orders_insert
after insert on Orders
for each row
begin
set @old_price_sum=0;
set @old_amount_sum=0;
set @old_price_avg=0;
set @old_orders_cnt=0;
select ifnull(price_sum,0),ifnull(amount_sum,0),ifnull(price_avg,0),ifnull(order_cnt,0)
from Order_mv
where product_name=new.product_name
into @old_price_sum,@old_amount_sum,@old_price_avg,@old_orders_cnt;
set @new_price_sum=@old_price_sum+new.price;
set @new_amount_sum=@old_amount_sum+new.amount;
set @new_orders_cnt=@old_orders_cnt+1;
set @new_price_avg=@new_price_sum/@new_orders_cnt;
replace into Order_mv
values(new.product_name,@new_price_sum,@new_amount_sum,@new_price_avg,@new_orders_cnt);
end;
$$
delimiter ;
3、update觸發器
復制代碼 代碼如下:
delimiter $$
create trigger tgr_Orders_update
before update on Orders
for each row
begin
set @old_price_sum=0;
set @old_amount_sum=0;
set @old_price_avg=0;
set @old_orders_cnt=0;
set @cur_price=0;
set @cur_amount=0;
select price,amount from Orders where order_id=new.order_id
into @cur_price,@cur_amount;
select ifnull(price_sum,0),ifnull(amount_sum,0),ifnull(price_avg,0),ifnull(order_cnt,0)
from Order_mv
where product_name=new.product_name
into @old_price_sum,@old_amount_sum,@old_price_avg,@old_orders_cnt;
set @new_price_sum=@old_price_sum-@cur_price+new.price;
set @new_amount_sum=@old_amount_sum-@cur_amount+new.amount;
set @new_orders_cnt=@old_orders_cnt;
set @new_price_avg=@new_price_sum/@new_orders_cnt;
replace into Order_mv
values(new.product_name,@new_price_sum,@new_amount_sum,@new_price_avg,@new_orders_cnt);
end;
$$
delimiter ;
4、delete觸發器
復制代碼 代碼如下:
delimiter $$
create trigger tgr_Orders_delete
after delete on Orders
for each row
begin
set @old_price_sum=0;
set @old_amount_sum=0;
set @old_price_avg=0;
set @old_orders_cnt=0;
set @cur_price=0;
set @cur_amount=0;
select price,amount from Orders where order_id=old.order_id
into @cur_price,@cur_amount;
select ifnull(price_sum,0),ifnull(amount_sum,0),ifnull(price_avg,0),ifnull(order_cnt,0)
from Order_mv
where product_name=old.product_name
into @old_price_sum,@old_amount_sum,@old_price_avg,@old_orders_cnt;
set @new_price_sum=@old_price_sum - old.price;
set @new_amount_sum=@old_amount_sum - old.amount;
set @new_orders_cnt=@old_orders_cnt - 1;
if @new_orders_cnt>0 then
set @new_price_avg=@new_price_sum/@new_orders_cnt;
replace into Order_mv
values(old.product_name,@new_price_sum,@new_amount_sum,@new_price_avg,@new_orders_cnt);
else
delete from Order_mv where [email protected];
end if;
end;
$$
delimiter ;
5、這裡delete觸發器有一個bug，就是在一種產品的最後一個訂單被刪除的時候，Order_mv表的更新不能實現，不知道這算不算是mysql的一個bug。當然，如果這個也可以直接用sql語句生成數據，而導致的直接後果就是執行效率低。
復制代碼 代碼如下:
-> insert into Order_mv
-> select product_name ,sum(price),sum(amount),avg(price),count(*) from Orders
-> group by product_name;
