SQL Server Execution Plans - Red Gate Software

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Figure 6.10 Chapter 6: Cursor Operations Finally, Query 5 closes the cursor and Query 6 de-allocates it, removing the cursor from the tempdb. CLOSE CurrencyList DEALLOCATE CurrencyList Listing 6.5 Figure 6.11 236
Physical operators Chapter 6: Cursor Operations When we execute the same script, using the actual execution plan, we find that it doesn't mirror the estimated plan. Instead, we see the plan shown in Figure 6.12. Figure 6.12 This simple plan is repeated 15 times, once for each row of data added to the cursor. The slight discrepancy between the actual number of rows, 15, and the estimated 14 rows you'll see in the ToolTip is caused by a minor disparity between the actual data and the statistics. One interesting thing to note is that no cursor icons are present in the plan. Instead, the one cursor command immediately visible, FETCH CURSOR, is represented by the generic T-<strong>SQL</strong> operator icon. This is because all the physical operations that occur with a cursor are represented by the actual operations being performed, and the FETCH is roughly equivalent to the SELECT statement. Hopefully, this execution plan demonstrates why a dynamic cursor may be costly to the system. It's performing a Clustered Index Insert, as well as the reads necessary to return the data to the cursor. It performs these actions as each of the 15 separate FETCH statements are called. The same query, outside a cursor, would return a very simple, one-step execution plan, as shown in Figure 6.13. Figure 6.13 237
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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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SQL Server Execution Plans - Red Gate Software

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