分组查询一例
在分组查询的select列表里面列只能为groupby里面的列,否则只能放在聚合函数里面。那么查询出来的信息就不完整,下面通过下面该查询让更多的列被查询出来。
input为商品入库表,total为数量,unitprice为单价,product_id为外键引用自input_categories表
[id] [int] IDENTITY(1,1) NOT NULL,
[product_id] [int] NOT NULL,
[unitprice] [float] NULL,
[total] [int] NULL,
input_categories位商品表(productname为商品名称):
[id] [int] IDENTITY(1,1) NOT NULL,
[productname] [nvarchar](50) NOT NULL)
现在要查询的是每一种商品最后一次入库的单价,以及该种商品的总和。
先看看两个表的数据先:
可用通过以下查询实现:
![](https://images.cnblogs.com/OutliningIndicators/ExpandedBlockStart.gif)
(
select *,ran=row_number() over(partition by productname order by id desc)
from
(select c.id,b.productname,b.total,c.unitprice from
(select productname,sum(total) as total from
(select i.id,ic.productname,i.unitprice,i.total
from input as i,input_categories as ic where i.product_id=ic.id) t
group by productname) b,(select i.id,ic.productname,i.unitprice,i.total
from input as i,input_categories as ic where i.product_id=ic.id) c
where b.productname=c.productname) h
)g
where g.ran<=1
下面来分解一下该查询:
1.因为两个表有主外键关系,所以通过联合查询,把两张表合二为一。
select i.id,ic.productname,i.unitprice,i.total
from input as i,input_categories as ic where i.product_id=ic.id
2.然后进行分组统计
select productname,sum(total) as total from
(select i.id,ic.productname,i.unitprice,i.total
from input as i,input_categories as ic where i.product_id=ic.id) t
group by productname
3.分组后信息只剩下productname,total了,为了让更多的信息包涵进来和可以进行一次连接查询(步骤2和步骤1的连接查询)
select c.id,b.productname,b.total,c.unitprice from
(select productname,sum(total) as total from
(select i.id,ic.productname,i.unitprice,i.total
from input as i,input_categories as ic where i.product_id=ic.id) t
group by productname) b,(select i.id,ic.productname,i.unitprice,i.total
from input as i,input_categories as ic where i.product_id=ic.id) c
where b.productname=c.productname
4.通过row_number()来插入一个序列。
select *,ran=row_number() over(partition by productname order by id desc)
from
(select c.id,b.productname,b.total,c.unitprice from
(select productname,sum(total) as total from
(select i.id,ic.productname,i.unitprice,i.total
from input as i,input_categories as ic where i.product_id=ic.id) t
group by productname) b,(select i.id,ic.productname,i.unitprice,i.total
from input as i,input_categories as ic where i.product_id=ic.id) c
where b.productname=c.productname) h
)g
5.最后,搞定最后一次入库的单价,id最大的ran刚好为1,所以筛选一下ran=1的记录就OK了。
大功告成拉,oh yeah!!