1. Reinhard Flügel
Possiblities and Limitations of System-Versioned Temporal Tables beyond the Basics

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3. About Me Reinhard Flügel (r.fluegel@fluegel-se.de)
Freelancer (Programming C++,C#, Access, SQL-Sever since the early 90’s)
MCSE Data Platform, Business Intelligence, Data Management and Analytics (Charter)
My way to System-Versioned Tables (New Project in October 2016; Project manager: We use Temporal Tables in a DWH-Project, but when we load the data we plan to set the valid times for all tables to a specific value.)

4. Agenda Short Introduction System-Versioned Temporal Tables
Manipulate Data with versioning switched off
Query multiple System-Versioned tables
Views on System-Versioned tables

5. Short Introduction System-Versioned Temporal Tables

6. From the Microsoft article: https://docs. microsoft
System-versioning for a table is implemented as a pair of tables, a current table and a history table. Within each of these tables, the following two additional datetime2 columns are used to define the period of validity for each row:
Period start column: The system records the start time for the row in this column, typically denoted as the SysStartTime column.
Period end column: The system records the end time for the row in this column, typically denoted at the SysEndTime column.
The current table contains the current value for each row. The history table contains each previous value for each row, if any, and the start time and end time for the period for which it was valid.

7. Sample: CREATE TABLE dbo.Employee (
[EmployeeID] int NOT NULL PRIMARY KEY CLUSTERED
, [Name] nvarchar(100) NOT NULL
, [Position] varchar(100) NOT NULL
, [Department] varchar(100) NOT NULL
, [Address] nvarchar(1024) NOT NULL
, [AnnualSalary] decimal (10,2) NOT NULL
, [ValidFrom] datetime2 (2) GENERATED ALWAYS AS ROW START
, [ValidTo] datetime2 (2) GENERATED ALWAYS AS ROW END
, PERIOD FOR SYSTEM_TIME (ValidFrom, ValidTo) )
WITH (SYSTEM_VERSIONING = ON (HISTORY_TABLE = dbo.EmployeeHistory));

9. Remark: The history table is page compressed.
The above statement creates although an index on the history table.
CREATE CLUSTERED INDEX [ix_EmployeeHistory] ON [dbo].[EmployeeHistory] (
[ValidTo] ASC,
[ValidFrom] ASC )
Different index strategy:
Illustrate the use of a Clustered Columnstore index on the history table with an additional Nonclustered Index.

10. Remark: Information on system-versioned temporal tables:
Select * from sys.tables
(temporal_type, temporal_type_desc, history_table_id)
Select * from sys.columns
(generated_always_type, generated_always_type_desc, ishidden)
Select * from sys.periods
Demo: Create system-versioned table based on Microsoft article)
01-01 – TableFromMSArticle
Demo: (Show infos on system-versioned table)
01-02 – InfoONTable

11. Manipulate Data with versioning switched off

12. Modifying Data in a System-Versioned Temporal Table
Articles:
Modifying Data in a System-Versioned Temporal Table
Temporal Table System Consistency Checks
Data Consistency Check
Before SYSTEM_VERSIONING is set to ON and as part of any DML operation, the system performs the following check: SysEndTime ≥SysStartTime
Marko Zivkovic: Temporal tables in SQL Server

13. Switch Versioning OFF Switch Versioning ON
ALTER TABLE <table, sysname, tablename> SET (SYSTEM_VERSIONING = OFF);
Switch Versioning ON
ALTER TABLE <table, sysname, tablename> SET (SYSTEM_VERSIONING = ON (HISTORY_TABLE = <table, sysname, tablename>History, DATA_CONSISTENCY_CHECK = ON ));

14. Demo: Prepare Table – PrepareTable History Table: Demo: (Update not auto-generated columns in the history table) – UpdateHistoryTableColumnNotGenerated – UpdateHistoryTableColumnNotGenerated Demo: (Update auto-generated columns in the history table) – UpdateHistoryTableColumnGenerated Actual Table: Demo: Update not auto-generated columns in the actual table UpdateActualTableColumnNotGenerated Demo: Update auto-generated columns in the actual table – UpdateActualTableColumnGenerated – UpdateActualTableColumnGenerated Demo: Use DATA_CONSISTENCY_CHECK = OFF – PrepareTable – SetVersioningONWithCHECK_ON – SetVersioningONWithCHECK_OFF Queries

15. Summary To Update Data in System-Versioned temporal tables the Versioning has to be switched of. For Updating data in the actual table Period for SYSTEM_Time has to be dropped, when preserving the Valid Times, or when updating the times. DATA_CONSISTENCY_CHECK kann be turned off, but on your own risk (Depending on the data, it can be substantially faster) Demo shows what can be done, but I have not tested it in practice.

16. Query multiple System-Versioned tables

17. Querying Data in a System-Versioned Temporal Table
Article:
Querying Data in a System-Versioned Temporal Table
Without the use of FOR SYSTEM_TIME only actual tables are used.
Demo: Basic queries without FOR SYSTEM_TIME, with FOR SYSTEM_TIME ALL and
FOR SYSTEM_TIME AS OF
in Queries

18. Demo: Query non temporal table with FOR SYSTEM_TIME CreateNonTemporalTable QueryNonTemporalTableForSYSTEM_TIME Demo: Prepare tables CreateDemoTables Demo: Query two temporal tables (for the same date) QueriesOnTwoTemporalTablesSameDate Demo: Query two temporal tables (for not the same date) QueriesOnTwoTemporalTablesNotSameDate Demo: Use a CTE UseCTE_Version UseCTE_Version2 Demo: Use a Scalar function without use of SYSTEM_TIME Create funcScalar_RemarkForIDNoSYSTEM_TIME Use funcScalar_RemarkForIDNoSYSTEM_TIME Demo: Use a Scalar function witht use of SYSTEM_TIME Create funcScalar_RemarkForIDWITH_SYSTEM_TIME Use funcScalar_RemarkForIDWITH_SYSTEM_TIME

19. Demo: Use an inline table valued function with and without use of SYSTEM_TIME Create inline table valued functions Use inline table valued functions Demo: Use a multistatement table valued function witht and without use of SYSTEM_TIME Create multistatement table valued functions Use multistatement table valued functions

20. Summary There is no magic
The Clause FOR SYSTEM_TIME has effect only on the table it follows directly
It only acts as a Filter for the referenced Time
It does not prevent logically invalid results
Use in a CTE or a function is similar
Use of the Clause FOR SYSTEM_Time not directly following a
System-Versioned temporal table RESULTS IN AN ERROR

21. Views on System-Versioned tables

22. Querying Data in a System-Versioned Temporal Table
Article:
Querying Data in a System-Versioned Temporal Table
Using views with AS-OF sub-clause in temporal queries
Using views is very useful in scenarios when complex point-in time analysis is required. A common example is generating a business report today with the values for previous month. Usually, customers have a normalized database model which involves many tables with foreign key relationships. Answering the question how data from that normalized model looked like at a point in the past can very challenging, since all tables change independently, on their own cadence. In this case, the best option is to create a view and apply the AS OF sub-clause to the entire view. Using this approach allows you to decouple modeling of the data access layer from point-in time analysis as SQL Server will apply AS OF clause transparently to all temporal tables that participate in view definition. Furthermore, you can combine temporal with non-temporal tables in the same view and AS OF will be applied only to temporal ones. If view does not reference at least one temporal table, applying temporal querying clauses to it will fail with an error.

23. Demo: View on non temporal table CreateViewNonTemporalTableAndQueryWithSYSTEM_TIME Demo: Query views on two system-versioned tables CreateViewONTemporalTables QueryViewWithSYSTEM_TIME QueryViewWithSYSTEM_TIME_Interval CreateVIEWWithJoinOnWithSYSTEM_TIME QueryViewWITHJoinOnWithSYSTEM_TIME Demo: Query views including inline table valued functions CreateViewWithInlineTBV_WITHOUT_SYSTEM_TIME UseViewWithInlineTBV_WITHOUT_SYSTEM_TIME CreateViewWithInlineTBV_WITH_SYSTEM_TIME UseViewWithInlineTBV_WITH_SYSTEM_TIME

24. Demo: Query views including multistatement table valued functions CreateViewWithIMultiTBV_WITHOUT_SYSTEM_TIME UseViewWithMultiTBV_WITHOUT_SYSTEM_TIME CreateViewWithIMultiTBV_WITH_SYSTEM_TIME UseViewWithIMultiTBV_WITH_SYSTEM_TIME Demo: Query view including a CTE and scalar functions with use and without use FOR SYSTEM_TIME – CreateViewWithCTEAndScalarFunctions UseViewWithCTEAndScalarFunctions

25. Important to remember:
datetime2(0) = ' :00:00'
datetime2(0) = ' :00:00'
SELECT * from [dbo].[DemoViewTemporalMultiTables] FOR SYSTEM_TIME AS
WHERe IDPK = 1
UNION ALL
SELECT * from [dbo].[DemoViewTemporalMultiTables] FOR SYSTEM_TIME AS
-- IS NOT
SELECT * from [dbo].[DemoViewTemporalMultiTables] FOr SYSTEM_TIME BETWEEN @ReferenceDateYesterday where IDPK=1
My Opinion: For Views only FOR SYSTEM_TIME AS OF should be allowed

26. Summary
Applying SYSTEM_TIME to a non System-Versioned View leads to an error.
Applying SYSTEM_TIME to a SYSTEM-Versioned Table based on a single table works like expected
A View can be build with a FOR SYSTEM_TIME clause, but than it can not be called with FOR SYSTEM_TIME
Applying FOR SYSTEM_TIME to a view referencing multiple temporal tables works as expected.

27. If a View is based on multiple temporal tables and one uses FOR SYSTEM_TIME AS OF the View cannot be called with FOR SYSTEM_TIME AS Of Use of table valued functions in a view leads for Inline TBVF‘s to unexpected behaviour. For multistatement TBVF‘s the FOR SYSTEM_TIME clause does not propagate to the function. This allows constructs to use a function to get results for a different date than the base view. CTE‘s and scalar funtions work as expected.

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