SQL Query to Find Most Effective Data

Question

I want to write query for find most effective rows. I have these tables:

Sellers
Id   Name
1    Mark
2    Julia
3    Peter

Stocks
 Id   SellerId   ProductCode   StockCount
 1       1         30A            10
 2       2         20A             4
 3       1         20A             2
 4       3         42B             3

And there sqlfiddle http://sqlfiddle.com/#!6/fe5b1/1/0

My Intent find optimum Seller for stock.

If client want 30A, 20A and 42B products. I need return to "Mark" and "Peter" because Mark have both product(30A and 20A), so not need there Julia.

How can i solve this in sql ?

Answer 1

Got it to work with the help of temporary tables

SELECT
  s.SellerId,
  ProductList = STUFF((
                       SELECT ',' + ProductCode FROM Stocks
                        WHERE s.SellerId = Stocks.SellerId
                        ORDER BY ProductCode FOR XML PATH('')
                       )
                      , 1, 1, ''), COUNT(*) AS numberOfProducts
INTO #tmptable
FROM
  Stocks s
WHERE
  s.ProductCode IN ('30A','20A','42B')
  AND s.StockData > 0
GROUP BY s.SellerId;

/*this second temp table is necessary, so we can delete from one of them*/
SELECT * INTO #tmptable2 FROM #tmptable; 

DELETE t1 FROM #tmptable t1
WHERE EXISTS (SELECT 1 FROM #tmptable2 t2
               WHERE t1.SellerId != t2.SellerId
                 AND t2.ProductList LIKE '%' + t1.ProductList + '%'
                 AND t2.numberOfProducts > t1.numberOfProducts)
;

SELECT Name FROM #tmptable t INNER JOIN Sellers ON t.SellerId = Sellers.Id;

UPDATE:

Please have a try with static tables:

CREATE TABLE tmptable (SellerId int, ProductList nvarchar(max), numberOfProducts int);

same for tmpTable2. Then change above code to

INSERT INTO tmpTable
SELECT
  s.SellerId,
  ProductList = STUFF((
                       SELECT ',' + ProductCode FROM Stocks
                        WHERE s.SellerId = Stocks.SellerId
                        ORDER BY ProductCode FOR XML PATH('')
                       )
                      , 1, 1, ''), COUNT(*) AS numberOfProducts
FROM
  Stocks s
WHERE
  s.ProductCode IN ('30A','20A','42B')
  AND s.StockData > 0
GROUP BY s.SellerId;

INSERT INTO tmpTable2 SELECT * FROM tmpTable;

DELETE t1 FROM tmptable t1
WHERE EXISTS (SELECT 1 FROM tmptable2 t2
               WHERE t1.SellerId != t2.SellerId
                 AND t2.ProductList LIKE '%' + t1.ProductList + '%'
                 AND t2.numberOfProducts > t1.numberOfProducts)
;

SELECT * FROM tmpTable;
DROP TABLE tmpTable, tmpTable2;