1. Module 7 Designing Queries for Optimal Performance

2. Module Overview Considerations for Optimizing Queries for Performance Refactoring Cursors into Queries Extending Set-Based Operations

3. Lesson 1: Considerations for Optimizing Queries for Performance Overview of Query Logical Flow Using the Query Optimizer to Process Queries Guidelines for Building Efficient Queries Considerations for Creating User-Defined Functions Considerations for Using User-Defined Functions Considerations for Determining Temporary Storage Discussion: Optimizing a Query

4. Aggregate Query Non-Aggregate Query Overview of Query Logical Flow From and Join From and Join Rows Where Select Order By Order By Result Set Result Set Grouping and Aggregation Grouping and Aggregation Having Result Set Result Set Result Set Result Set Order By Order By

5. Using the Query Optimizer to Process Queries Query Optimizer Query Database Schema Query Plan

6. Guidelines for Building Efficient Queries Test query variations for performance Avoid query hints Use correlated subqueries to improve performance Use table-valued, user-defined functions as derived tables Avoid unnecessary GROUP BY columns; use a subquery instead Use CASE expressions to include variable logic in a query Divide joins into temporary tables when you query large tables Favor set-based logic over procedural or cursor logic Avoid using a scalar user-defined function in the WHERE clause

7. Considerations for Creating User-Defined Functions Consider relevant factors when indexing the results of the function Troubleshoot and test the function Create each function to accomplish a single task Qualify object names referenced by a function with the appropriate schema name Identify the type of function to be used User-Defined Function SELECT FROM WHERE

8. Considerations for Using User-Defined Functions User-Defined Function Integrate the user-defined function into the query plan as a join Consider the balance between performance and maintainability Avoid using a user-defined function if performance suffers tremendously

9. To achieve optimal tempdb performance: Set the recovery model of tempdb to SIMPLE Allow for tempdb files to automatically grow Set the file growth increment to a reasonable size Preallocate space for all tempdb files Create multiple files to maximize disk bandwidth Make each data file of the same size Load the tempdb database on a fast I/O subsystem Consider transferring the tempdb database to a different subsystem or disk Set the recovery model of tempdb to SIMPLE Allow for tempdb files to automatically grow Set the file growth increment to a reasonable size Preallocate space for all tempdb files Create multiple files to maximize disk bandwidth Make each data file of the same size Load the tempdb database on a fast I/O subsystem Consider transferring the tempdb database to a different subsystem or disk Considerations for Determining Temporary Storage

10. Discussion: Optimizing a Query What is the primary consideration when handling repetitive tasks against a set of data? What will be the effect of having the tempdb database on the same disk or Logical Unit Number (LUN) as the transaction log file? Can disciplined code formatting and using naming standards improve query execution performance? Explain the benefits of disciplined code formatting and using naming standards.

11. Lesson 2: Refactoring Cursors into Queries Building a T-SQL Cursor Common Scenarios for Cursor-Based Operations Demonstration: How To Refactor a Cursor Discussion: Using Cursors Guidelines for Using Result Set-Based Operations Selecting Appropriate Server-Side Cursors Selecting Appropriate Client-Side Cursors

12. Building a T-SQL Cursor Use the OPEN statement to execute the SELECT statement 3 3 Use the FETCH NEXT INTO statement to retrieve values from the next row 4 4 Use the DECLARE CURSOR statement to define the SELECT statement 2 2 Issue the CLOSE and DEALLOCATE statements to close the cursor 5 5 Declare the variables for the data to be returned by the cursor 1 1 Each FETCH in a cursor has the same performance as a SELECT statement Cursors use large amounts of memory Cursors can cause locking problems in the database Cursors consume network bandwidth Each FETCH in a cursor has the same performance as a SELECT statement Cursors use large amounts of memory Cursors can cause locking problems in the database Cursors consume network bandwidth Why Cursors Are Slow

13. ProblemDescriptionSolutionCursor Usage Complex Logic Difficult to translate into a set-based solution Refactor the logic as a data driven query Rare Dynamic Code Iteration Requires DDL codeUse Transact-SQL cursorsAlways List Denormalization Converts a vertical list of values to a single comma-delimited horizontal list or string User set-based operations, recursion, or XML queries Sometimes Crosstab Query Building Difficult to build by using SQL Server Use series of case expressions or PIVOT syntax Never* Cumulative Totals Needs to be calculated within SQL Server and written to a table Use Transact-SQL cursorsSometimes Hierarchical Tree Navigation Needs recursive examination of each node Use set-based methods that use stored procedures or UDFs Never Common Scenarios for Cursor-Based Operations *Constructing a dynamic cross-tab query requires using a cursor to build the columns for the dynamic SQL

14. Demonstration: How To Refactor a Cursor In this demonstration, you will see how to: Refactor a cursor

15. Discussion: Using Cursors List some of the disadvantages of using a cursor. What is the major issue with using a cursor in modern relational databases? What kind of a problem is best solved by using a cursor? Discuss your own experiences with cursors.

16. Guidelines for Using Result Set-Based Operations Use queries that affect groups of rows rather than one row at a time Avoid making inline calls to scalar UDF in large result sets Limit query cardinality as early as possible Use result sets instead of cursor-based processes to minimize I/O Minimize the use of conditional branches inside queries

17. Selecting Appropriate Server-Side Cursors Static Cursor Forward-Only Cursor Keyset-Driven Cursor Server-Side Cursors Dynamic Cursor

18. Selecting Appropriate Client-Side Cursors Network latency. Client cursors use more network resources Additional cursor types. Client cursors support only a limited functionality Positioned updates. Client-side cursors will not reflect database changes until the changes are synchronized with the database Memory usage. The client computer should have enough memory to handle the size of the entire result set Network latency. Client cursors use more network resources Additional cursor types. Client cursors support only a limited functionality Positioned updates. Client-side cursors will not reflect database changes until the changes are synchronized with the database Memory usage. The client computer should have enough memory to handle the size of the entire result set Considerations for Using Client-Side Cursors Client Data Access Libraries That Support Client-Side Cursors ODBC ADO ADO.NET- SqlClient OLE DB

19. Lesson 3: Extending Set-Based Operations What Are Common Table Expressions? Comparing CTE with Other SQL Tuning Techniques Demonstration: How To Use a CTE Discussion: Using Common Table Expressions Demonstration: How To Perform Recursive Queries with CTE Discussion: Recursion with CTEs Introduction to Ranking Functions Demonstration: How To Use Ranking Functions To Rank Rows What Are PIVOT and UNPIVOT Operators? Demonstration: How To Use PIVOT and UNPIVOT Options To Convert Data

20. ParameterDescription expression_name Is used to reference the query that is using the CTE Can be any valid identifier column_name Specifies the name of a column for the CTE Is taken from the result set in case no column_name parameters are specified CTE_query_definition Specifies the SELECT statement that forms the result set Is followed by a SELECT, INSERT, UPDATE, or DELETE query What Are Common Table Expressions? A CTE is a named temporary result set based on a regular SELECT query. The following table describes the syntax parameters for a CTE

21. Comparing CTE with Other SQL Tuning Techniques A CTE does not store data anywhere until you actually execute it whereas in a temporary table, the data is stored in the tempdb database You must call a CTE immediately after stating whereas you can call a temporary table over and over again from within a statement Compute, Order By (without a TOP), INTO, Option, FOR XML, and FOR BROWSE are all not allowed in CTE whereas these options are supported in a temporary table A CTE does not store data anywhere until you actually execute it whereas in a temporary table, the data is stored in the tempdb database You must call a CTE immediately after stating whereas you can call a temporary table over and over again from within a statement Compute, Order By (without a TOP), INTO, Option, FOR XML, and FOR BROWSE are all not allowed in CTE whereas these options are supported in a temporary table CTE vs Temporary Table In the CTE, the result set will be evaluated just once when a query is executed whereas in a subquery the result set will be evaluated every time a query is executed In the CTE, the result set will be evaluated just once when a query is executed whereas in a subquery the result set will be evaluated every time a query is executed CTE vs Subquery

22. Demonstration: How To Use a CTE In this demonstration, you will see how to: Create and use a CTE

23. Discussion: Using Common Table Expressions How does a CTE differ from a #Temp table? Can you execute two or more queries against a CTE? How does a CTE differ from a derived table? Can you build indexes or constraints on a CTE?

24. Demonstration: How To Perform Recursive Queries with CTEs In this demonstration, you will see how to: Perform recursive queries with CTEs

25. Discussion: Recursion with CTEs What is the maximum number of recursive levels in a common table expression (CTE)? What is the default number of recursions in a recursive common table expression? Assuming that each recursion adds only one row to the results, how many rows will be returned with OPTION MAXRECURSION(100)? Select an option from the following: 99 100 101

26. Introduction to Ranking Functions Ranking functions return a ranking value for each row in a partition FunctionDescription RANK Returns the rank of each row within the partition of a result set NTILE Distributes the rows in an ordered partition into a specified number of groups DENSE_RANK Returns the rank of rows within the partition of a result set, without any gaps in the ranking ROW_NUMBER Returns the sequential number of a row within a partition of a result set, starting at 1 for the first row in each partition

27. Demonstration: How To Use Ranking Functions To Rank Rows In this demonstration, you will see how to: Use Ranking Functions to rank rows

28. ParameterDescription table_source Is the name of the table that you need to pivot aggregate_function Is a system or user-defined aggregate function that applies to the specified value_colum pivot_column Is the source column that provides the values for the new crosstab column column_list Is a list of values of pivot_column to display as the crosstab column headers table_alias Is the name of the resulting result set PIVOT is used to generate crosstab queries in which values are converted to column headers. UNPIVOT is used to convert column headers to values. The following table describes the parameters in the PIVOT and UNPIVOT syntax. What Are PIVOT and UNPIVOT Operators?

29. Demonstration: How To Use PIVOT and UNPIVOT Options To Convert Data In this demonstration, you will see how to: Use PIVOT and UNPIVOT options to convert data

30. Notes Page Over-flow Slide. Do Not Print Slide. See Notes pane.

31. Lab 7: Designing Queries for Optimal Performance Exercise 1: Optimizing Query Performance Exercise 2: Refactoring Cursors into Queries Estimated time: 60 minutes Logon Information Virtual machine User name Password NYC-SQL1 Administrator Pa$$w0rd

32. Lab Scenario You are a lead database designer at QuantamCorp. You are working on the Human Resources Vacation and Sick Leave Enhancement (HR VASE) project that is designed to enhance the current HR system of your organization. This system is based on the QuantamCorp sample database in SQL Server 2008. The main goals of the HR VASE project are as follows: Provide managers with current and historical information about employee vacation and sick leave. Grant view rights to individual employees to view their vacation and sick leave balances. Provide permission to selected employees in the HR department to view and update the vacation and sick leave details of employees. Grant the HR manager with the view and update rights to all the data. You are working on a project to integrate HR VASE with an intranet site which is used to send email broadcast to external people. The details of email recipients are loaded from QuantamCorp HR VASE into the system named Baldwin2. Recently, a number of functions at Baldwin2 receive many complaints about the performance. You are assigned to help fine tune the performance of the SQL used by those functions.

33. Module Review and Takeaways Review Questions Real-World Issues and Scenarios

34. Notes Page Over-flow Slide. Do Not Print Slide. See Notes pane.