SQL Server Features That Will Blow Your Mind!
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How many lines of code does it take to generate a running total? How would you find a value in the next row of data – without using a cursor or loop? How can you efficiently store rows of data with a lot of optional fields, and how can you quickly find which of those rows have values? And how can you eliminate locking without resorting to dirty reads? SQL Server has answers for all of these questions, and none requires more than a few lines of code. Give me an hour, and I will blow your mind!
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SQL Server Features That Will Blow Your Mind!
- 1. SQL SERVER FEATURES THAT WILL BLOW YOUR MIND! Ed Leighton-Dick
- 2. ABOUT ME Email: ed@leightondick.com Blog: edleightondick.com Twitter: @eleightondick
- 3. AGENDA • Window Functions • Sparse Columns • Filtered Indexes • Snapshot Isolation
- 5. WINDOW FUNCTIONS • First group introduced in SQL Server 2005 • Use OVER clause to create dynamic windows in the dataset
- 6. OVER() • OVER(ORDER BY expressionList) • OVER(PARTITION BY expressionList1 ORDER BY expressionList2)
- 8. AGGREGATE FUNCTIONS • COUNT, COUNT_BIG • SUM • AVG • MAX • MIN • STDEV, STDEVP • CHECKSUM_AGG • VAR, VARP
- 9. RANKING FUNCTIONS • ROW_NUMBER • RANK • DENSE_RANK • NTILE
- 10. ANALYTIC FUNCTIONS • LAG • LEAD • FIRST_VALUE • LAST_VALUE • CUME_DIST • PERCENTILE_CONT • PERCENTILE_DISC • PERCENT_RANK
- 11. RANGE AND ROWS • RANGE: Number of distinct values • ROWS: Number of rows • RANGE: Always uses disk-based worktable • ROWS: Worktable in memory if less than 10K rows
- 12. SPARSE COLUMNS
- 14. FILTERED INDEXES
- 17. WHY DO WE USE NOLOCK? Image link: http://www.flixya.com/files-photo/k/e/v/kevinkr500-1881624.jpg
- 18. WHY DO WE USE NOLOCK? • Removes blocking that exists in the default READ COMMITTED isolation
- 19. THAT’S GOOD, RIGHT? • Locks exist to prevent uncommitted data from being read (“dirty reads”) • Data sets can change during your query without locks • “Halloween Problem”: Rows can move during query, showing up in results twice
- 21. SNAPSHOT ISOLATION • Introduced in SQL Server 2005 • Available in all editions • More precisely referred to as “row versioning” • Not related to database snapshots!
- 23. HOW IT WORKS • Without snapshot isolation
- 24. HOW IT WORKS • With snapshot isolation tempdb version store
- 25. HOW IT WORKS: RESOURCES • 14-byte XSN added to each row • Not added to existing rows until modified • Row copied to version store in tempdb upon modification • Row retained in version store until all transactions with lower XSNs are finished
- 26. SNAPSHOT ISOLATION VS RCSI • RCSI • Implicit once turned on • Affects each statement individually • Snapshot isolation • Explicit • SET TRANSACTION ISOLATION LEVEL SNAPSHOT • Affects entire transaction as a unit
- 27. REVIEW • Window Functions • Sparse Columns • Filtered Indexes • Snapshot Isolation
- 28. QUESTIONS? Email: ed@leightondick.com Blog: edleightondick.com Twitter: @eleightondick
- 29. THANK YOU FOR ATTENDING! ~ Please remember to fill out your comment cards ~
Editor's Notes
- CUME_DIST (Cumulative Distribution), PERCENT_RANK – Relative position w/in group of values – Returns percentile/percent PERCENTILE_CONT – Percentile based on a continuous distribution of values – Returns interpolated value (may not exist) PERCENTILE_DISC – Percentile based on discrete distribution of values – Returns actual value