INNER JOIN vs INNER JOIN (SELECT . FROM)

Question

Is there any difference in terms of performance between these two versions of the same query?

--Version 1
SELECT p.Name, s.OrderQty
FROM Product p
INNER JOIN Sal         


        

Answer 1

You did the right thing by checking from query plans. But I have 100% confidence in version 2. It is faster when the number off records are on the very high side.

My database has around 1,000,000 records and this is exactly the scenario where the query plan shows the difference between both the queries. Further, instead of using a where clause, if you use it in the join itself, it makes the query faster :
SELECT p.Name, s.OrderQty
FROM Product p
INNER JOIN (SELECT ProductID, OrderQty FROM SalesOrderDetail) s on p.ProductID = s.ProductID WHERE p.isactive = 1

The better version of this query is :

SELECT p.Name, s.OrderQty
FROM Product p
INNER JOIN (SELECT ProductID, OrderQty FROM SalesOrderDetail) s on p.ProductID = s.ProductID AND p.isactive = 1

(Assuming isactive is a field in product table which represents the active/inactive products).