Question

I have a SQL database of products from different suppliers, so the same product could appear multiple times with different prices.

Is it possible to select all of the products that have more than 4 prices, so bascially all of the rows which have more than 4 rows with the same ID?

Answer 1

Yes, GROUP on the identificator for your item, and specify the number of prices to count in a HAVING clause, something like this :

SELECT ItemID, COUNT(Price) FROM itemTBL GROUP BY ItemID HAVING COUNT(Price) >= 4

You can then use this to later filter and get more information:

SELECT Item.*, Category.Name, Filter.NumPrices from itemTBL AS Item 
INNER JOIN categoryTBL as Category ON Item.CategoryID = Category.CategoryID
INNER JOIN (SELECT ItemID, COUNT(Price) AS NumPrices FROM itemTBL GROUP BY ItemID HAVING COUNT(Price) >= 4) AS Filter on Item.ItemID = Filter.ItemID