Using multiple and interdepended CROSS-APPLY across multiple tables - sql

Question

How can I use either CROSS APPLY (or INNER JOIN) to get data from one table based on the values in other tables?
I.e. I have the following tables:
Table Descriptions:
ProdID
Description
TrackNum
361
Test 1
499
388
Test 2
003
004
5599
238
Test 3
499
361
Test 10
555
004
Test 40
555
Table Products:
ProdID
ProductName
Price
361
P1
5.00
388
P2
5.00
004
P3
12.00
238
P4
6.00
515
P5
7.00
636
P6
7.00
775
P7
7.00
858
P8
8.00
Table Invoices:
ProdID
TrackNum
InvoiceID
361
499
718
388
199
718
004
499
718
238
499
718
361
555
333
004
555
444
361
111
444
388
222
333
616
116
565
717
116
565
361
003
221
388
003
221
004
5599
728
What I need my query to do is to:
Go into Invoices table first, and get only records that matches specified InvoiceID and TrackNum;
Then go into Products table and get only rows that have matches on ProdID between the data I pulled out in Step #1 and the data existis in the Products table.
Then finally get all columns from the Descriptions table, but only for the rows which I got in the Step #2 and which matches on ProdID.
What I need to have at the end is something like this (if I get more columns that is fine, but I do not want to get more rows):
ProdID
Description
TrackNum
361
Test 1
499
004
5599
238
Test 3
499
I have following query (and I have tried using INNER JOIN and CROSS APPLY) - but it returns me more rows than I need:
SELECT * FROM [Descriptions] AS [DES]
CROSS APPLY
(
select * from [Invoices] AS [INV] where [INV].[TrackNum] = '499' AND [INV].[InvoiceID] = '718'
) [INV]
CROSS APPLY
(
select * from [Products] AS [GP]
WHERE [GP].[ProdID] = [INV].[ProdID]
) [GP2]
WHERE
[DES].[ProdID] = [GP2].[ProdID]
order by [DES].[ProdID] asc

Answer 1

SELECT
*
FROM
invoices AS i
LEFT JOIN
descriptions AS d
ON d.prodid = i.prodid
AND d.tracknum = i.tracknum -- you don't have this, but I think it's required.
LEFT JOIN
products AS p
ON p.prodid = i.prodid
WHERE
i.invoiceid = 718
AND i.tracknum = 499
ORDER BY
i.prodid
One thing that concerns me is that both the invoices and descriptions have a column named tracknum, but your query and expected data indicate that you don't want to include that in the join? That's very confusing and either a poor column name, or a mistake in your query and example results.

Answer 2

Based on what you describe you want the following, start with your Invoices table and a where clause to get the right rows, then join on Products and Descriptions.
I'm also guessing that you want to match the Description on TrackNum? Since it appears you have a unique Description per ProdId/TrackNum combination.
select [INV].[ProdID], [DES].[Description], [INV].[TrackNum]
from [Invoices] as [INV]
inner join [Products] as [GP] on [GP].[ProdID] = [INV].[ProdID]
inner join [Descriptions] on [DES].[ProdID] = [GP].[ProdID] and [DES].[TrackNum] = [INV].[TrackNum]
where [INV].[TrackNum] = '499' AND [INV].[InvoiceID] = '718'
order by [DES].[ProdID] asc;
Note: You normally only use a 'CROSS APPLY' for queries where you want to run/evaluate something per row in your main table.

Answer 3

In this case the Inner Join is sufficient. You don't need to use Cross Apply