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    <p>I consider as a good practice to use sub-queries allowing to reduce the overall number of joining operations and the amount of the columns in the block GROUP BY. Therefore, I will tell you at once that the first query is definitely more efficient.</p> <p><strong>Queries:</strong></p> <pre><code>SELECT t.OrderYear , t.CustomerID , t.CustomerOrderAmt , p.FirstName , p.LastName FROM ( SELECT OrderYear = YEAR(OrderDate) , CustomerID , CustomerOrderAmt = COUNT(CustomerID) FROM Sales.SalesOrderHeader GROUP BY YEAR(OrderDate) , CustomerID HAVING COUNT(CustomerID) &gt; 1 ) t JOIN ( SELECT p.FirstName , p.LastName , c.CustomerID FROM Person.Person p JOIN Sales.Customer c ON c.PersonID = p.BusinessEntityID ) p ON t.CustomerID = p.CustomerID ORDER BY t.OrderYear , t.CustomerID </code></pre> <p>vs</p> <pre><code>SELECT Orderdate = YEAR(so.OrderDate) , so.CustomerID , CustomerOrderAmt = COUNT(so.CustomerID) , FirstName = MAX(p.FirstName) , LastName = MAX(p.LastName) FROM Sales.SalesOrderHeader so JOIN Sales.Customer c ON so.CustomerID = c.CustomerID JOIN Person.Person p ON c.PersonID = p.BusinessEntityID GROUP BY YEAR(so.OrderDate) , so.CustomerID HAVING COUNT(so.CustomerID) &gt; 1 </code></pre> <p><strong>Query cost:</strong></p> <p><img src="https://i.stack.imgur.com/M901V.png" alt="Query cost"></p> <p><strong>Execution time:</strong></p> <pre><code>-- first query SQL Server Execution Times: CPU time = 94 ms, elapsed time = 395 ms. -- second query SQL Server Execution Times: CPU time = 140 ms, elapsed time = 480 ms. </code></pre>
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