mysql触发器实现oracle物化视图示例代码

oracle数据库支持物化视图--不是基于基表的虚表，而是根据表实际存在的实表，即物化视图的数据存储在非易失的存储设备上。
下面实验创建ON COMMIT 的FAST刷新模式，在mysql中用触发器实现insert , update , delete 刷新操作
1、基础表创建，Orders 表为基表，Order_mv为物化视图表

代码如下：

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触发器

代码如下：

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触发器

代码如下：

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触发器

代码如下：

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、这里delete触发器有一个bug，就是在一种产品的最后一个订单被删除的时候，Order_mv表的更新不能实现，不知道这算不算是mysql的一个bug。当然，如果这个也可以直接用sql语句生成数据，而导致的直接后果就是执行效率低。

代码如下：

-> insert into Order_mv 
-> select product_name ,sum(price),sum(amount),avg(price),count(*) from Orders 
-> group by product_name;