Sql server windowing functions

2. Enrique Catalá Bañuls•Computer engineer•Mentor at SolidQ in the relational engine team•Microsoft Technical Ranger•Microsoft Active Professional•Microsoft Certified Trainer© 2012 SolidQecatala@solidq.comTwitter: @enriquecatala

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6. Window Functions•Window function• function applied to a set of rows defined by a windowdescriptor and returns a single value for each rowfrom the underlying query•Window descriptor• Define which rows will be used with the function© 2012 SolidQ

8. The past, the present and the future•The SQL 2000 way• SQL Server 2000 does not provide any syntax tosupport windowing functions•The SQL 2005 way• SQL Server 2005 to 2008R2 introduced a partialimplementation of the windowing functions using theOVER clause•The SQL 2012 way• SQL Server 2012 will have an almost completeimplementation of the windowing functions© 2012 SolidQ

9. The SQL 2005-2008R2 way•SQL Server 2005 introduces• OVER clause (partially implemented)• New window functionso ROW_NUMBER()o RANK()o DENSE_RANK()o NTILE()•SQL Server 2008/2008R2 added no newimplementations in this particular area© 2012 SolidQ

11. The SQL 2012 way• SQL Server 2012 are getting close to the fullimplementation of Windowing functions• SQL Server 2012 introduces:• OVER clause almost completeo Order byo Window Frame• 8 new window functionso LAG(), LEAD()o FIRST_VALUE(), LAST_VALUE()o CUME_DIST()o PERCENT_RANK()o PERCENTILE_DISC(), PERCENTILE_COUNT()© 2012 SolidQ

14. Why do we need windows functions?• Why do we need windows functions?• What if we want to get the sum and the valuecolumn? (group and detail)• If we are in SQL 2005/2008/2008R2…am i correct withthis approach?select id_table, value,sum(value) as [sum(value)]from table1 group by id_tableMsg 8120, Level 16, State 1, Line 1Column table1.value is invalid in the select list becauseit is not contained in either an aggregate function or theGROUP BY clause.id_table value1 12 12 23 13 23 3SUM(value)136id_table value sum(value)1 1 12 1 32 2 33 1 63 2 63 3 6Select sum(value) as [sum(value)]from table1 group by id_table© 2012 SolidQ

15. Why do we need windows functions?•Now we know that the OVER clause exists…•This must be our solutionselect id_table,value,sum(value) over(partition by id_table)from table1id_table value sum(value)1 1 12 1 32 2 33 1 63 2 63 3 6© 2012 SolidQ

22. Key concepts: Slicing/Framing• B1 and B2 can be• UNBOUNDED PRECEDING• UNBOUNDED FOLLOWING• CURRENT ROW• For “ROWS” clause onlyo <scalar expression> PRECEDINGo <sclara expression> FOLLOWING• Note• B1 <= B2 or NULL will be returnedo Except in COUNT() that 0 will be returned© 2012 SolidQ

24. New windowing functions• New analytic functions in SQL 2012• offset• LAG()• LEAD()• FIRST_VALUE()• LAST_VALUE()• Distribution• PERCENT_RANK()• CUME_DIST()• PERCENTILE_CONT()• PERCENTILE_DIST()© 2012 SolidQ

28. Performance: IN-MEMORY vs ONDISK• Directly affected by Window Spool Operator• Used to store the framing data• In-memory vs disk-based worktable• In-memory worktable• Fastest• Prerequisites: Framing defined using ROWS and workingwith <10k rows• Disk-based worktable• Default• Used when the window was defined using RANGE• Used when the windows was defined using ROWS and theframe has more than 10k rows© 2012 SolidQ

29. Performance: Indexing•Index order by the window partitioningelements and then by the order elements•Include the rest of the columns•Optimized execution operators:1. Scan2. Segment3. Window spool4. Aggregate© 2012 SolidQ© 2012 SolidQ

31. Why almost complete?• RANGE only supports• UNBOUNDED PRECEDING• UNBOUNDED FOLLOWING• CURRENT ROW• Ranking functions does not support framing:• ROW_NUMBER, RANK, NTILE,DENSE_RANK,PERCENTILE_DIST, PERCENTILE_CONT• Not implemented• WINDOW aliases• Clauses: NULLs FIRST and NULLs LAST© 2012 SolidQ

32. Objectives of this session•Introduction•The past, the present and the future•Window Functions• Why do we need window functions?• Syntax• Performance• Why almost complete?•Q&A32 |

33. THANK YOU!Enrique Catalá BañulsMentor, SolidQMAP 2012 – Microsoft Technical Ranger – Microsoft Certified Trainerecatala@solidq.comTwitter: @enriquecatala