How to query Products by Opportunity?

Hi Suraj,
You can use OpportunityLineItem to traverse from Opportunity to PricebookEntry and Product..

something like this query :

SELECT Id, Name, Account.Name, (SELECT Quantity, UnitPrice, TotalPrice, PricebookEntry.Name, PricebookEntry.Product2.Family FROM OpportunityLineItems) FROM Opportunity WHERE Id = :YourOppId

Thanks.