sql 2008 Study for three -----Merge
1.语法
MERGE <tatget table> [AS <alias>]
USING
(
<source query>
)
WHEN {[NOT] MATCHED | <expression> THEN <action statement> [<additional WHEN clauses>,[.....n]}
2.实例 参考sqlserver2008 高级编程
创建一张累计销售表
create table sales.monthyrollup
(
year smallest not null,
month tinyint not null,
productid int not null foreign key references procudtion.product(productid),
qtysold int not null constraint pkyearmonthproductid primary key(year,month,product)
);
--查询当月第一天的数据
MERGE sales.monthlyrollup as smr
(
select soh.orderdate,sod.productid,sum(sod.orderqty)as qtysold from sales.salesorderheader soh
join sales.salesorderdetail sod on soh.salesorderid=sod.salesorderid
where soh.orderdate>='2003-08-01' and son.orderdate<'2003-08-02'
group by soh.orderdate,sod,productid
) as s
on (s.productid=smr.productid)--这里的on可以理解为if
when matched then
update set smr.qtysold =smr.qtysold+s.qtysold
when not matched then
insert (year,month,productid,qtysold) values(date part(yy,s.orderdate),date part(m,s.orderdate),s.productid,s.qtysold);
--查询当月第二天的数据
MERGE sales.monthlyrollup as smr
(
select soh.orderdate,sod.productid,sum(sod.orderqty)as qtysold from sales.salesorderheader soh
join sales.salesorderdetail sod on soh.salesorderid=sod.salesorderid
where soh.orderdate>='2003-08-02' and son.orderdate<'2003-08-03'
group by soh.orderdate,sod,productid
) as s
on (s.productid=smr.productid)
when matched then
update set smr.qtysold =smr.qtysold+s.qtysold
when not matched then
insert (year,month,productid,qtysold) values(date part(yy,s.orderdate),date part(m,s.orderdate),s.productid,s.qtysold);
会发现数据没有新增那么多，只是将在第一天没有的productid新增到里面，而有的产品id会直接累加。
这里可以新建作业，写成存储过程，每天晚上去更新表，第二天早上就可以得到所需的数据。