Trivadis TechEvent 2017 SQL Server 2016 Temporal Tables by Willfried Färber

BASLE BERN BRUGG DÜSSELDORF FRANKFURT A.M. FREIBURG I.BR. GENEVA

HAMBURG COPENHAGEN LAUSANNE MUNICH STUTTGART VIENNA ZURICH

SQL Server 2016 Temporal Tables

Willfried Färber – [email protected]

Agenda

1. Overview of SQL Server 2016 temporal tables

2. Data Definition for temporal tables

3. Data Manipulation with temporal tables

4. Usage Scenarios

Why – History Tables

• Auditing all data changes and performing data

forensics when necessary

• Reconstructing state of the data as of any time in

the past

• Calculating trends over time – Anomaly Detection

• Maintaining a slowly changing dimension for

decision support applications

• Recovering from accidental data changes and

application errors

What is a Temporal Table?

• A temporal table is a table for which a PERIOD definition exists and which

contains system columns with a datatype of datetime2 into which the period

of validity is recorded by the system, and which has an associated history

table into which the system records all prior versions of each record with

their period of validity.

• With a temporal table, the value of each record at any point in time can be

determined, rather than just the current value of each record. A temporal

table is also referred to as a system-versioned table.

Temporal Tables

Automatically keeps track of changed data

• Along with period of validity

• Available in all editions of SQL Server (from the Express!)

• Available in SQL Azure

• SQL ANSI 2011 compliant

• Provide native support for “as-of-time” queries

• Transparent to existing applications (if needed)

• Integrated with existing features (eg: Partitioning, Hekaton)

• Integrated with new features (eg: Stretch Database)

Insert, Update, Delete

New clauses – Data Definition

CREATE TABLE Department ( DeptID int NOT NULL PRIMARY KEY CLUSTERED , DeptName varchar(50) NOT NULL , ManagerID INT NULL , ParentDeptID int NULL , SysStartTime datetime2 GENERATED ALWAYS AS ROW START HIDDEN NOT NULL , SysEndTime datetime2 GENERATED ALWAYS AS ROW END HIDDEN NOT NULL , PERIOD FOR SYSTEM_TIME (SysStartTime, SysEndTime)

) WITH ( SYSTEM_VERSIONING = ON (HISTORY_TABLE = dbo.DepartmentHistory) ) ;

GENERATED ALWAYS AS ROW START

GENERATED ALWAYS AS ROW END

PERIOD FOR SYSTEM_TIME

SYSTEM_VERSIONING = ON

BEGIN TRANSACTION

-- Add required period columns and designationALTER TABLE dbo.Person ADD

DateTimeStart DATETIME2(0) GENERATED ALWAYS AS ROW START NOT NULLCONSTRAINT DFT_person_datetimeStart DEFAULT('19000101 00:00:00'),

DateTimeEnd DATETIME2(0) GENERATED ALWAYS AS ROW END NOT NULLCONSTRAINT DFT_person_datetimeEnd DEFAULT('99991231 23:59:59'),

PERIOD FOR SYSTEM_TIME (DateTimeStart, DateTimeEnd);

-- Remove temporary DEFAULT constraintsALTER TABLE dbo.Person

DROP CONSTRAINT DFT_person_datetimeStart, DFT_person_datetimeEnd;

-- Turn system versioning onALTER TABLE dbo.Person

SET ( SYSTEM_VERSIONING = ON ( HISTORY_TABLE = dbo.PersonHistory ) );

COMMIT TRANSACTION;

System generated temporal table

SQL Server 2016 Temporal Tables9 30-Oct-17

Creating through SSMS

Querying temporal data

FOR predicate


Expression Qualifying Rows

AS OF <date_time> SysStartTime < = date_time AND SysEndTime >

date_time

FROM <start_date_time>

TO <end_date_time>

SysStartTime < end_date_time AND SysEndTime >

start_date_time

BETWEEN

<start_date_time> AND

<end_date_time>

SysStartTime < = end_date_time AND SysEndTime >

start_date_time

CONTAINED IN

(<start_date_time>,

<end_date_time>)

SysStartTime > = start_date_time AND SysEndTime < =

end_date_time

ALL all rows

New clauses – AS OF

DECLARE @datetime AS DATETIME2 = '20161108 20:00:00'

SELECT *FROM dbo.Person FOR SYSTEM_TIME AS OF @datetimeORDER BY DateTimeStart ASC,

DateTimeEnd ASC

Clauses SYSTEM_TIME allow to realize temporal queries transparently for user and applications.

FOR SYSTEM_TIME AS OF @datetime

Reference: http://sqlmag.com/sql-server/first-look-system-versioned-temporal-tables-part-2-querying-data-and-optimization-conside (Itzik Ben Gan)

sysEnd > @datetime

sysStart <= @datetime


Returns a table with a rows containing

the values that were actual (current) at

the specified point in time in the past.

http://sqlmag.com/sql-server/first-look-system-versioned-temporal-tables-part-2-querying-data-and-optimization-conside

FOR SYSTEM_TIME FROM @Start TO @End


sysStart < @End

sysEnd > @Start


Returns a table with the values for all row

versions that were active within the

specified time range, regardless of

whether they started being active before

the <start_date_time> parameter value for

the FROM argument or ceased being

active after the <end_date_time>

parameter value for the TO argument.


FOR SYSTEM_TIME BETWEEN @Start AND @End


sysStart <= @End

sysEnd > @Start


Same as above in the FOR SYSTEM_TIME

FROM <start_date_time> TO

<end_date_time> description, except the

table of rows returned includes rows that

became active on the upper boundary

defined by the <end_date_time> endpoint.


FOR SYSTEM_TIME CONTAINED IN (@Start,@End)


sysStart >= @Start

sysEnd <= @End


Returns a table with the values for all row

versions that were opened and closed within

the specified time range defined by the two

datetime values for the CONTAINED IN

argument.


Considerations for resource use

• A temporal table must have a primary key defined in order to correlate records between the

current table and the history table, and the history table cannot have a primary key defined.

• The SYSTEM_TIME period columns used to record the SysStartTime and SysEndTime values

must be defined with a datatype of datetime2.

• If the name of a history table is specified during history table creation, you must specify the

schema and table name.

• By default, the history table is PAGE compressed.

• If current table is partitioned, the history table is created on default file group because partitioning

configuration is not replicated automatically from the current table to the history table.

• Temporal and history tables cannot be FILETABLE and can contain columns of any

supported datatype other than FILESTREAM since FILETABLE and FILESTREAM allow data

manipulation outside of SQL Server and thus system versioning cannot be guaranteed.

More work, but much better …


Define the history table by your self

• Define a separate filegroup

• Use a special schema – iE. History

• Maybe use Column Store Index

• Maybe use Partitions

• Create Clustered Index on the file table

CREATE CLUSTERED INDEX uidx_<tablename>_hist ON <tablename>(ValidTo ASC, ValidFrom ASC, EmployeeID ASC)

ON [History];

Limitations…

• TRUNCATE TABLE is not supported while SYSTEM_VERSIONING is ON

• Direct modification of the data in a history table is not permitted.

• ON DELETE CASCADE and ON UPDATE CASCADE are not permitted on the current table. In

other words, when temporal table is referencing table in the foreign key relationship

(corresponding to parent_object_id in sys.foreign_keys) CASCADE options are not allowed. To

work around this limitation, use application logic or after triggers to maintain consistency on delete

in primary key table (corresponding to referenced_object_id in sys.foreign_keys). If primary key

table is temporal and referencing table is non-temporal, there’s no such limitation.

• INSTEAD OF triggers are not permitted on either the current or the history table and AFTER

triggers are permitted only on the current table.

• Regular queries only affect data in the current table. To query data in the history table, you must

use temporal queries.

Security for temporal tables


• Creating a temporal table requires CONTROL rights

• DBOwner has Control rights in the database

• When SYSTEM_VERSIONING is ON users cannot alter history data regardless of

their actual permissions on current or the history table. This includes both data and

schema modifications

• Querying history data requires SELECT permission on the history table

• Merely because a user has SELECT permission on the current table does not

mean that they have SELECT permission on the history table

https://msdn.microsoft.com/en-us/library/mt604469.aspx

https://msdn.microsoft.com/en-us/library/mt604469.aspx

Willfried Färber

Principal Consultant

Tel. +41 58 459 50 11

[email protected]

30.10.2017 SQL Server 2016 Temporal Tables21

Source code for the demos

SQL Server 2016 Temporal Tables22 30.10.2017

Trivadis TechEvent 2017 SQL Server 2016 Temporal Tables by Willfried Färber

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