sql cross join - 有人找到了什么用途？

Question

今天,在使用sql server进行10年开发的第一次中,我在生产查询中使用了交叉连接.我需要将结果集填充到报表中,并发现具有creative where子句的两个表之间的交叉连接是一个很好的解决方案.我想知道在交叉连接的生产代码中有什么用处？

更新:托尼安德鲁斯发布的代码非常接近我使用交叉联接的代码.相信我,我理解使用交叉连接的含义,并不会轻易做到这一点.我很高兴最终使用它(我是一个书呆子) - 有点像我第一次使用完全外连接的时候.

感谢大家的答案!这是我使用交叉连接的方式:

SELECT  CLASS, [Trans-Date] as Trans_Date,
SUM(CASE TRANS
     WHEN 'SCR' THEN [Std-Labor-Value]
     WHEN 'S+' THEN [Std-Labor-Value]
     WHEN 'S-' THEN [Std-Labor-Value]
     WHEN 'SAL' THEN [Std-Labor-Value]
     WHEN 'OUT' THEN [Std-Labor-Value]
     ELSE 0
END) AS [LABOR SCRAP],
SUM(CASE TRANS
     WHEN 'SCR' THEN  [Std-Material-Value]
     WHEN 'S+' THEN [Std-Material-Value]
     WHEN 'S-' THEN  [Std-Material-Value]
     WHEN 'SAL' THEN [Std-Material-Value]
     ELSE 0
END) AS [MATERIAL SCRAP], 
SUM(CASE TRANS WHEN 'RWK' THEN [Act-Labor-Value] ELSE 0 END) AS [LABOR REWORK],
SUM(CASE TRANS 
     WHEN 'PRD' THEN  [Act-Labor-Value]
     WHEN 'TRN' THEN  [Act-Labor-Value]
     WHEN 'RWK' THEN  [Act-Labor-Value]
     ELSE 0 
END) AS [ACTUAL LABOR],
SUM(CASE TRANS 
     WHEN 'PRD' THEN  [Std-Labor-Value]
     WHEN 'TRN' THEN   [Std-Labor-Value]
     ELSE 0 
END) AS [STANDARD LABOR],
SUM(CASE TRANS 
     WHEN 'PRD' THEN  [Act-Labor-Value] - [Std-Labor-Value]
     WHEN 'TRN' THEN  [Act-Labor-Value] - [Std-Labor-Value]
     --WHEN 'RWK' THEN  [Act-Labor-Value]
     ELSE 0 END) -- - SUM([Std-Labor-Value]) -- - SUM(CASE TRANS WHEN 'RWK' THEN [Act-Labor-Value] ELSE 0 END) 
AS [LABOR VARIANCE] 
FROM         v_Labor_Dist_Detail
where [Trans-Date] between @startdate and @enddate
    --and CLASS = (CASE @class WHEN '~ALL' THEN CLASS ELSE @class END)
GROUP BY  [Trans-Date], CLASS
UNION  --REL 2/6/09 Pad result set with any missing dates for each class. 
select distinct [Description] as class,  cast([Date] as datetime) as [Trans-Date], 0,0,0,0,0,0 
FROM Calendar_To_Fiscal cross join PRMS.Product_Class
where cast([Date] as datetime) between @startdate and @enddate and
not exists (select class FROM v_Labor_Dist_Detail vl where [Trans-Date] between @startdate and @enddate
                    and vl.[Trans-Date] = cast(Calendar_To_Fiscal.[Date] as datetime)
                    and vl.class= PRMS.Product_Class.[Description]
                GROUP BY [Trans-Date], CLASS)
order by [Trans-Date], CLASS

Answer 1

交叉连接的典型合法用途是显示例如按产品和地区划分的总销售额的报告.如果没有在区域R中销售产品P,那么我们希望看到一行为零,而不是仅显示一行.

select r.region_name, p.product_name, sum(s.sales_amount)
from regions r
cross join products p
left outer join sales s on  s.region_id = r.region_id
                        and s.product_id = p.product_id
group by r.region_name, p.product_name
order by r.region_name, p.product_name;

Answer 2

我经常遇到的一个用途是将记录分成几个记录,主要用于报告目的.

想象一个字符串,其中每个字符代表相应小时内的某个事件.

ID | Hourly Event Data
1  | -----X-------X-------X--
2  | ---X-----X------X-------
3  | -----X---X--X-----------
4  | ----------------X--X-X--
5  | ---X--------X-------X---
6  | -------X-------X-----X--

现在,您需要一份报告,显示当天发生的事件数量.用一张ID为1到24的表格交叉加入表格,然后运用你的魔法......

SELECT
   [hour].id,
   SUM(CASE WHEN SUBSTRING([data].string, [hour].id, 1) = 'X' THEN 1 ELSE 0 END)
FROM
   [data]
CROSS JOIN
   [hours]
GROUP BY
   [hours].id

=>

1,  0
2,  0
3,  0
4,  2
5,  0
6,  2
7,  0
8,  1
9,  0
10, 2
11, 0
12, 0
13, 2
14, 1
15, 0
16, 1
17, 2
18, 0
19, 0
20, 1
21, 1
22, 3
23, 0
24, 0