SQL Server Windowing
Functions
Enrique Catalá Bañuls
Mentor, SolidQ
MAP 2012 – Microsoft Technical Ranger – Microsoft Certified Trainer
ecatala@solidq.com
Twitter: @enriquecatala
© 2012 SolidQ

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

3© 2012 SolidQ
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Real Practices for
the Real World
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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&A
5 |© 2012 SolidQ

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

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&A
7 |© 2012 SolidQ

The past, the present and the future
•The SQL 2000 way
• SQL Server 2000 does not provide any syntax to
support windowing functions
•The SQL 2005 way
• SQL Server 2005 to 2008R2 introduced a partial
implementation of the windowing functions using the
OVER clause
•The SQL 2012 way
• SQL Server 2012 will have an almost complete
implementation of the windowing functions
© 2012 SolidQ

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

The SQL 2005-2008R2 way
•OVER clause
•Two different implementations depending on
type of windowing
• Aggregate window functions does not provide the
ORDER BY clause
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The SQL 2012 way
• SQL Server 2012 are getting close to the full
implementation of Windowing functions
• SQL Server 2012 introduces:
• OVER clause almost complete
o Order by
o Window Frame
• 8 new window functions
o LAG(), LEAD()
o FIRST_VALUE(), LAST_VALUE()
o CUME_DIST()
o PERCENT_RANK()
o PERCENTILE_DISC(), PERCENTILE_COUNT()
© 2012 SolidQ

OVER clause syntax
•SQL Server 2005/2008/R2
• SQL Server 2012
© 2012 SolidQ

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&A
13 |© 2012 SolidQ

Why do we need windows functions?
• Why do we need windows functions?
• What if we want to get the sum and the value
column? (group and detail)
• If we are in SQL 2005/2008/2008R2…am i correct with
this approach?
select id_table, value,
sum(value) as [sum(value)]
from table1 group by id_table
Msg 8120, Level 16, State 1, Line 1
Column 'table1.value' is invalid in the select list because
it is not contained in either an aggregate function or the
GROUP BY clause.
id_table value
1 1
2 1
2 2
3 1
3 2
3 3
SUM(value)
1
3
6
id_table value sum(value)
1 1 1
2 1 3
2 2 3
3 1 6
3 2 6
3 3 6
Select sum(value) as [sum(value)]
from table1 group by id_table
© 2012 SolidQ

Why do we need windows functions?
•Now we know that the OVER clause exists…
•This must be our solution
select id_table,
value,
sum(value) over(partition by id_table)
from table1
id_table value sum(value)
1 1 1
2 1 3
2 2 3
3 1 6
3 2 6
3 3 6
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New syntax to solve old
problems
• Partitioning
• Ordering
• Slicing/framing
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Key concepts: All together
Partition
UNBOUNDED
FOLLOWING
UNBOUNDED
PRECEDING
CURRENT
ROW
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Key concepts
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Key concepts: Partition
•Partition is like a group of
rows with similar
“characteristics” inside a set
© 2012 SolidQ

Key concepts: Partition
•Partition is like a group of
rows with similar
“characteristics” inside a set
© 2012 SolidQ

Key concepts: Slicing/Framing
• RANGE/ROWS
• ROWS | RANGE BETWEEN <B1> AND <B2>
• ROWS | RANGE <B1>
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Key concepts: Slicing/Framing
• B1 and B2 can be
• UNBOUNDED PRECEDING
• UNBOUNDED FOLLOWING
• CURRENT ROW
• For “ROWS” clause only
o <scalar expression> PRECEDING
o <sclara expression> FOLLOWING
• Note
• B1 <= B2 or NULL will be returned
o Except in COUNT() that 0 will be returned
© 2012 SolidQ

Key concepts: All together
Partition
UNBOUNDED
FOLLOWING
UNBOUNDED
PRECEDING
CURRENT
ROW
© 2012 SolidQ

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

DEMO 1: NEW FUNCTIONS
AND SYNTAX
Basics on framing, RANGE vs ROWS, new window functions
© 2012 SolidQ

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&A
26 |© 2012 SolidQ

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&A
27 |© 2012 SolidQ

Performance: IN-MEMORY vs ON
DISK
• 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 working
with <10k rows
• Disk-based worktable
• Default
• Used when the window was defined using RANGE
• Used when the windows was defined using ROWS and the
frame has more than 10k rows
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Performance: Indexing
•Index order by the window partitioning
elements and then by the order elements
•Include the rest of the columns
•Optimized execution operators:
1. Scan
2. Segment
3. Window spool
4. Aggregate
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© 2012 SolidQ

DEMO 2: PERFORMANCE
Running Totals, in memory vs on disk, …
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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

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&A
32 |

THANK YOU!
Enrique Catalá Bañuls
Mentor, SolidQ
MAP 2012 – Microsoft Technical Ranger – Microsoft Certified Trainer
ecatala@solidq.com
Twitter: @enriquecatala