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

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

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

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

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 product_name=@old.name;
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。

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