SQL Server Execution Plans - Red Gate Software

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Chapter 5: Controlling Execution Plans with Hints Normally, the optimizer will determine the order in which the joins occur, rearranging them as it sees fit. However, the optimizer can make incorrect choices when the statistics are not up to date, when the data distribution is less than optimal, or if the query has a high degree of complexity, with many joins. In the latter case, the optimizer may even time out when trying to rearrange the tables because there are so many of them for it to try to deal with. Using the FORCE ORDER hint you can make the optimizer use the order of joins as you have defined them in the query. This might be an option if you are fairly certain that your join order is better than that supplied by the optimizer, or if you're experiencing timeouts. SELECT pc.Name AS ProductCategoryName , ps.Name AS ProductSubCategoryName , p.Name AS ProductName , pdr.Description , pm.Name AS ProductModelName , c.Name AS CultureName , d.FileName , pri.Quantity , pr.Rating , pr.Comments FROM Production.Product AS p LEFT JOIN Production.ProductModel AS pm ON p.ProductModelID = pm.ProductModelID LEFT JOIN Production.ProductSubcategory AS ps ON p.ProductSubcategoryID = ps.ProductSubcategoryID LEFT JOIN Production.ProductInventory AS pri ON p.ProductID = pri.ProductID LEFT JOIN Production.ProductReview AS pr ON p.ProductID = pr.ProductID LEFT JOIN Production.ProductDocument AS pd ON p.ProductID = pd.ProductID LEFT JOIN Production.Document AS d ON pd.DocumentNode = d.DocumentNode LEFT JOIN Production.ProductCategory AS pc ON ps.ProductCategoryID = pc.ProductCategoryID LEFT JOIN Production.ProductModelProductDescriptionCulture AS pmpdc ON pm.ProductModelID = pmpdc.ProductModelID 192
Listing 5.17 Chapter 5: Controlling Execution Plans with Hints LEFT JOIN Production.ProductDescription AS pdr ON pmpdc.ProductDescriptionID = pdr.ProductDescriptionID LEFT JOIN Production.Culture AS c ON c.CultureID = pmpdc.CultureID; Based on your knowledge of the data, you're confident that you've put the joins in the correct order. Figure 5.13 shows the current execution plan. Figure 5.13 Again, this plan is far too large to review on the page, but it gives you a good idea of its overall structure. Figure 5.14 shows an exploded view of just a few of the tables and the order in which they are being joined. 193
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SQL Handbooks SQL Server Execution
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First Edition 2008 Copyright Grant
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Chapter 2: Graphical Execution Plan
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Table Hints _______________________
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About the Author Grant Fritchey is
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Foreword I have attended many SQL S
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Introduction Every day, out in the
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If you are specifically looking for
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Some of the code may not work withi
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Chapter 1: Execution Plan Basics Wh
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The query optimizer Chapter 1: Exec
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Execution Plan Formats Chapter 1: E
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Getting Started Chapter 1: Executio
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SQL Server Execution Plans - Red Gate Software

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