Practical Uses and Optimization of New T-SQL Features in Microsoft SQL Server 2012 Tobias Ternstrom

DBI308

Program Manager, SQL Server

JanEngelsberg

janeng@microsoft.com

Agenda

Key generation

Calculations & Aggregations

Common tasks

Exceptions & Messages

Key generationUse cases:

Unique keys across multiple tablesCustomers & Employees ContactsClient-side/distributed-system key generationPrep files with related items for import

Options:GUIDsTable to manage the keysNEW: Sequences

Key generation

SQL Server 2012

Sequence Generators

New Database Object, similar to the IDENTITY propertySeparates number-generation from table/columnANSI SQL standard compliant implementation

CREATE SEQUENCE [ schema_name . ] sequence_name

[ AS

{ <built_in_integer_type> | <user-

defined_integer_type> } ]

[ START WITH <constant> ]

[ INCREMENT BY <constant> ]

[ MINVALUE <constant> | NO MINVALUE ]

[ MAXVALUE <constant> | NO MAXVALUE ]

[ CYCLE | NO CYCLE ]

[ CACHE [ <constant> ] | NO CACHE ]

NEXT VALUE FOR

[ schema_name . ] sequence_name

[ OVER (<over_order_by_clause>) ]

EXEC sp_sequence_get_range …

Key generation in action

• Guaranteed to be globally unique

• Can be made sequential• Caveats!

• Cannot be guessed (when not sequential)

• Use any data type for keys(for ex. strings)

• Can guarantee a continuous range of values (no wholes)• Including ranges

• Serializes number generation across transactions

• Supports all integer types, starting from TINYINT up to DECIMAL(38, 0)

• Supports range reservation

• Caching “knob” for performance tuning

• Large; requires 16 bytes storage

• Many systems don’t natively support GUIDs

• Causes fragmentation• Sequential generation

cannot be guaranteed even with NEWSEQUENTIALID()

• Access to the identifier is serialized across transactions• Performance issue

• Not native RDBMS functionality, more code

• Cannot guarantee a continuous range of values• E.g. can “lose”

values because of dirty shutdowns or rollbacks

GUIDs

Pros

Cons

Separate table Sequences

Exceptions & Messages

Use cases:Send progress updates to the applicationLog eventsRaise & handle exceptions

Options:RAISERRORxp_logeventLogging tableNEW: THROW

Exceptions & Messages

SQL Server 2012

New error handling with THROW

THROW <number>, <message>, <state>;Always aborts the batchBatch aborts if not in SET XACT_ABORT ON where it transaction-abortsDoes not automatically use sys.messagesIs even spelled correctly!

re-THROWBEGIN CATCH …; THROW;END CATCH

Exceptions & messages in action

• Flexible• Well known

• Logs events without sending a message to the client

• Multiple behaviors, easy to get it wrong

• Not supported on SQL Azure

RAISERROR

Pros

Cons

xp_logevent

• Flexible, supports the attributes you specify

• Transactions need to be managed so log records are not rolled back

Logging table

• Easy to use• Similar behavior

to other programming languages

• Re-throw capabilities

• Less flexible than RAISERROR

THROW

Calculations & Aggregations

Use cases:Include aggregations in detailsCumulative sum, averages etc.Reference other rows in a calculationFinding gaps, trends, etc.

Options:Imperative programming patternsCorrelated sub queriesNEW: Window Functions

SQL Server 2012

Calculations & Aggregations

Calculations across rows

Referencing same row is simple:

Transaction cost is $1.5/tran., what was the total amount?

Amount + 1.5 AS TotalAmount

What about other rows?Current bank balance?Current account balance?Number of days since last tran.?Amount of previous transaction?

TranId AccountId TranDate Amount

1 1 2011-12-19 120

2 2 2011-12-20 500

3 3 2011-12-21 430

4 1 2011-12-26 95

5 2 2011-12-27 50

6 3 2011-12-28 25

7 1 2012-01-02 250

8 2 2012-01-03 25

9 3 2012-01-04 5000

10 1 2012-01-09 75

3 trn. avg.

Window Functions

Calculate the average amount of the last 3 transactions

TranId AccountId TranDate Amount

1 1 2011-12-19 120

2 2 2011-12-20 500

3 3 2011-12-21 430

4 1 2011-12-26 95

5 2 2011-12-27 50

6 3 2011-12-28 25

7 1 2012-01-02 250

8 2 2012-01-03 25

9 3 2012-01-04 5000

10 1 2012-01-09 75

120.000

310.000

350.000

341.666

191.666

56.666

108.333

100.000

1758.3331700.000

The FRAMEWindow

PARTITIONThe FRAMEThe FRAMEThe FRAMEThe FRAMEThe FRAMEThe FRAMEWindow FRAME

Window Functions

Multiple partitions, e.g. for calculating the balance for different accounts

Balance

TranId AccountId TranDate Amount

1 1 2011-12-19 120

4 1 2011-12-26 95

7 1 2012-01-02 250

10 1 2012-01-09 75

13 1 2012-01-16 125

16 1 2012-01-23 175

2 2 2011-12-20 500

5 2 2011-12-27 50

8 2 2012-01-03 25

11 2 2012-01-10 125

120

215

465

540

665

840

500

550

575

700

Window PARTITIONs

Window PARTITIONs

Window FRAMEWindow FRAME

Window Functions

AggregationAVG, CHECKSUM_AGG, COUNT, COUNT_BIG, MIN, MAX, SUM, STDEV, STDEVP, VAR, VARPUser-defined CLR Aggregates (excl. windowing)

AnalyticalROW_NUMBER, NTILE, RANK, DENSE_RANK, CUME_DIST, PERCENT_RANK

DistributionPERCENTILE_CONT, PERCENTILE_DISC

OffsetLAG, LEAD, FIRST_VALUE, LAST_VALUE

Calculations & Aggregations in action

• Approach that is commonly used in other programming languages

• Follows the SQL set based paradigm

• Improved optimization• Easy to write• Following the SQL set

based paradigm

• Not set based• Only individual queries

are optimized, not the operation as a whole

• Many lines of code Higher risk for bugs

• Bad performance due to plan with N2 complexity solution

• Non-trivial to write

• Not always the optimal solution

• Not all queries can be easily rewritten to leverage window functions

Imperative approach

Pros

Cons

Correlated sub queries Window Functions

Common tasks

Use cases:Transform data to and from stringsConstructing date instancesHandle conversion errorsPaging

Options:Write yourselfNEW: Additional scalar functions

Common tasks

SQL Server 2012

New Scalar Functions

New conversion functions for all types:TRY_CONVERT(data_type[(length)], expression [,style])

TRY_CAST(expression AS data_type[(length)])

New conversion functions to and from strings:FORMAT(value, format [,culture])PARSE(string_value AS data_type [USING culture])TRY_PARSE(string_value AS data_type [USING culture])

Other functions:IIF(boolean_expr, true_value, false_value)CHOOSE(index, val1, val2,... [,valN])CONCAT(val1, val2,… [,val N])

New Scalar Functions

New date & time related functions:EOMONTH(date [, months_to_add])DATEFROMPARTS(year, month, day)TIMEFROMPARTS(hour, minutes, seconds, fractions, scale)DATETIME2FROMPARTS(year, month, day ,hour, minutes,

seconds, fractions, scale)DATETIMEFROMPARTS(year, month, day, hour, minutes,

seconds, milliseconds)SMALLDATETIMEFROMPARTS(year, month, day, hour, minutes)DATETIMEOFFSETFROMPARTS (year, month, day, hour, minute,

seconds, fractions, hour_offset, minute_offset,

precision)

Query Constructs / Dynamic SQL enhancements

OFFSET / FETCHSupport for paging result sets

Enforce contract for Result Sets for EXEC

SELECT ...ORDER BY ...

OFFSET <expr> ROWS FETCH NEXT <expr> ROWS ONLY

EXECUTE <proc|clr proc|remote proc|function> [WITH <execute_option>[,...n ]]{ RESULT SETS {UNDEFINED|NONE|(<result_sets_definition>)} }

<result_sets_definition> ::= { <result_set_definition> | AS OBJECT [<object_location>.] {table_name | view_name | tvf} | AS TYPE [schema_name.]table_type_name | AS FOR XML | (…) [,...n ]}

Common tasks in action

Questions

?

Related Content(DBI311) Microsoft SQL Server Data Tools: Database Development from Zero to Sixty(DBI409)SQL Server Columnstore Performance Tuning

(DBI21-HOL ) What's New in T-SQL for Microsoft SQL Server 2012 (DBI31-HOL) Getting Started with SQL Server Data Tools in Microsoft SQL Server 2012

(DBI07-TLC ) Microsoft SQL Server: Cloud on Your Terms - Optimized Productivity

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