1. It’s About Time : Temporal Table Support in SQL Server 2016/2017
Vern Rabe
RabeData, LLC
It’s About Time : Temporal Table Support in SQL Server 2016/2017

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5. Vern Rabe
Portland, OR independent consultant, trainer MCTA, MCDBA, MCSE, MCITP Co-VP Oregon PASS chapter Working with/focusing on SQL Server since 1993, starting with SQL Server 4.21a My first PC had a 10MB hard drive

6. Vern Rabe

7. What We’ll Cover
What are we trying to solve What is a temporal table Creating and altering SELECT enhancements SQL Server 2016 temporal table limitations What’s new in SQL Server 2017

8. Use Cases
Repeatable reports Changing validity periods Who made that change? (auditing) Monitoring business trends Repairing row-level corruption(not a replacement to BACKUP/RESTORE) Slowly Changing Dimension?

9. Definitions Temporal tables hold current and past versions of data
Defined in ISO SQL:2011
What’s a timestamp?
Instant, Interval (duration), Period (anchored duration)
System Period
Application Period
Bi-Temporal
Closed vs. Open ended Periods

10. Temporal Tables vs. CDC (Change Data Capture)
CDC can be at column level
CDC has less of a performance hit (Tlog)
CDC is eventually current
CDC relies on Agent
Reliability
CDC designed for short term use, e.g., for ETL incremental loads
Temporal Tables designed to be long term, for complete row history
Temporal Tables easy to query

11. SQL Server Temporal Table
Base (current) table with attached history table
Two datetime2 columns define System Period
UTC based
US – “CUT” (Coordinated Universal Time)
French – “TUC” (Temps Universel Coordonné)
System maintained
INSERTs – Base table gets System Period columns set to “Now” and No History table activity
UPDATEs – Base table row is copied to History table, terminated to “Now”. Base table row set to start “Now”
DELETEs –Base table row is moved to History, terminated to “Now”
Querying additions to T-SQL

12. Implementing in SQL Server
CREATE/ALTER TABLE
Two NOT NULL datetime2 columns to define period (any precision)
GENERATED ALWAYS AS ROW START
GENERATED ALWAYS AS ROW END
Optional HIDDEN
PERIOD FOR SYSTEM_TIME for these two columns (closed-open)
Table option SYSTEM_VERSIONING ON
Optionally specify history table name – schemas must match exactly
ALTER can apply to existing non-temporal table (migrating history)

13. Syntax
Basic CREATE • Specifying history table name • Specifying history table name for existing table – consistency check • ALTER existing base and history table •

14. Time Traveling Using T-SQL
FOR SYSTEM_TIME
AS OF <timestamp> •
FROM <start_ timestamp> TO <end_ timestamp> •
Closed-open
BETWEEN <start_ timestamp> AND <end_timestamp>
Closed-closed
CONTAINED IN (<start_ timestamp>, <end_ timestamp>)
Fully contained, closed-closed
Not ISO
ALL •
Recovering from accidental DELETE/UPDATE •

15. Metadata sys.tables sys.columns sys.periods •
temporal_type: 1=history, 2=current
temporal_type_desc:
HISTORY_TABLE (1)
SYSTEM_VERSIONED_TEMPORAL_TABLE (2)
history_table_id
sys.columns
generated_always_type: 1=start, 2=end
generated_always_desc:
AS_ROW_START
AS_ROW_END
NOT_APPLICABLE
sys.periods •
OBJECTPROPERTY & OBJECTPROPERTYEX
TableTemporalType: 1=history, 2=current
COLUMNPROPERTY
GeneratedAlwaysType
IsHidden

16. SQL Server 2016 Limitations
Base table must have PK History table cannot have PK History table must be in same database as current table Querying temporal tables over Linked Server not allowed No data modification directly on History tables No INSERT/UPDATE directly on SYSTEM_TIME columns

17. SQL Server 2016 Limitations (cont.)
Cannot be FILETABLE, cannot have FILESTREAM No constraints on history table (except DEFAULT, which is ineffective) In-Memory OLTP “mostly” implemented Truncate table not allowed No INSTEAD OF triggers No triggers on history table No history table chaining Manual changes to system clock can cause failures

18. New Features in SQL Server 2017
Limit life of history table contents System-versioned temporal tables now support CASCADE DELETE and CASCADE UPDATE

19. Summary
Several uses Repeatable reports Trend analysis Data audit Repair row-level data corruption Base + History Table System Period (not Application Period) Fully system maintained Easy to create, easy to query

20. Resources SQL:2011 temporal summary
Temporal Data and the Relational Model
C.J.Date
Hugh Darwen
Nikos A. Lorentzos
Developing Time-Oriented Database Applications in SQL
Richard T. Snodgrass

21. Thanks. Questions?
Vern Rabe
@VernRabe