Today, for the first time in 10 years of development with sql server I used a cross join in a production query. I needed to pad a result set to a report and found that a cross join between two tables with a creative where clause was a good solution. I was wondering what use has anyone found in production code for the cross join?
Update: the code posted by Tony Andrews is very close to what I used the cross join for. Believe me, I understand the implications of using a cross join and would not do so lightly. I was excited to have finally used it (I'm such a nerd) - sort of like the time I first used a full outer join.
Thanks to everyone for the answers! Here's how I used the cross join:
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
One use I've come across a lot is splitting records out into several records, mainly for reporting purposes.
Imagine a string where each character represents some event during the corresponding hour.
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--
Now you want a report which shows how many events happened at what day. Cross join the table with a table of IDs 1 to 24, then work your magic...
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
A typical legitimate use of a cross join would be a report that shows e.g. total sales by product and region. If no sales were made of product P in region R then we want to see a row with a zero, rather than just not showing a row.
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;
I have different reports that prefilter the recordset (by various lines of business within the firm), but there were calculations that required percentages of revenue firm-wide. The recordsource had to contain the firm total instead of relying on calculating the overall sum in the report itself.
Example: The recordset has balances for each client and the Line of Business the client's revenue comes from. The report may only show 'retail' clients. There is no way to get a sum of the balances for the entire firm, but the report shows the percentage of the firm's revenue.
Since there are different balance fields, I felt it was less complicated to have full join with the view that has several balances (I can also reuse this view of firm totals) instead of multiple fields made up sub queries.
Another one is an update statement where multiple records needed to be created (one record for each step in a preset workflow process).
Here's one, where the CROSS JOIN substitutes for an INNER JOIN. This is useful and legitimate when there are no identical values between two tables on which to join. For example, suppose you have a table that contains version 1, version 2 and version 3 of some statement or company document, all saved in a SQL Server table so that you can recreate a document that is associated with an order, on the fly, long after the order, and long after your document was rewritten into a new version. But only one of the two tables you need to join (the Documents table) has a VersionID column. Here is a way to do this:
SELECT DocumentText, VersionID =
(
SELECT d.VersionID
FROM Documents d
CROSS JOIN Orders o
WHERE o.DateOrdered BETWEEN d.EffectiveStart AND d.EffectiveEnd
)
FROM Documents
I've used a CROSS JOIN recently in a report that we use for sales forcasting, the report needs to break out the amount of sales that a sales person has done in each General Ledger account.
So in the report I do something to this effect:
SELECT gla.AccountN, s.SalespersonN
FROM
GLAccounts gla
CROSS JOIN Salesperson s
WHERE (gla.SalesAnalysis = 1 OR gla.AccountN = 47500)
This gives me every GL account for every sales person like:
SalesPsn AccountN 1000 40100 1000 40200 1000 40300 1000 48150 1000 49980 1000 49990 1005 40100 1005 40200 1005 40300 1054 48150 1054 49980 1054 49990 1078 40100 1078 40200 1078 40300 1078 48150 1078 49980 1078 49990 1081 40100 1081 40200 1081 40300 1081 48150 1081 49980 1081 49990 1188 40100 1188 40200 1188 40300 1188 48150 1188 49980 1188 49990
For charting (reports) where every grouping must have a record even if it is zero. (e.g. RadCharts)
I had combinations of am insolvency field from my source data. There are 5 distinct types but the data had combinations of 2 of these. So I created lookup table of the 5 distinct values then used a cross join for an insert statement to fill out the rest. like so
insert into LK_Insolvency (code,value)
select a.code+b.code, a.value+' '+b.value
from LK_Insolvency a
cross join LK_Insolvency b
where a.code <> b.code <--this makes sure the x product of the value with itself is not used as this does not appear in the source data.
I personally try to avoid cartesian product's in my queries. I suppose have a result set of every combination of your join could be useful, but usually if I end up with one, I know I have something wrong.
来源：https://stackoverflow.com/questions/523091/sql-cross-join-what-use-has-anyone-found-for-it