Trivadis TechEvent 2017 SQL Server 2016 Temporal Tables by Willfried Färber
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This is a presentation about SQL Server Temporal Tables held by Willfried Färber at the Trivadis TechEvent 2017.
![More work, but much better …
SQL Server 2016 Temporal Tables18 30-Oct-17
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];](https://image.slidesharecdn.com/sqlserver2016temporaltableswillfriedfrbertechevent2017-171101094414/85/Trivadis-TechEvent-2017-SQL-Server-2016-Temporal-Tables-by-Willfried-Farber-18-320.jpg)
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Trivadis TechEvent 2017 SQL Server 2016 Temporal Tables by Willfried Färber
- 1. 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 – BS [email protected]
- 2. Agenda 1. Overview of SQL Server 2016 temporal tables 2. Data Definition for temporal tables 3. Data Manipulation with temporal tables 4. Usage Scenarios
- 3. 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
- 4. 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.
- 5. 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)
- 7. 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
- 8. BEGIN TRANSACTION -- Add required period columns and designation ALTER TABLE dbo.Person ADD DateTimeStart DATETIME2(0) GENERATED ALWAYS AS ROW START NOT NULL CONSTRAINT DFT_person_datetimeStart DEFAULT('19000101 00:00:00'), DateTimeEnd DATETIME2(0) GENERATED ALWAYS AS ROW END NOT NULL CONSTRAINT DFT_person_datetimeEnd DEFAULT('99991231 23:59:59'), PERIOD FOR SYSTEM_TIME (DateTimeStart, DateTimeEnd); -- Remove temporary DEFAULT constraints ALTER TABLE dbo.Person DROP CONSTRAINT DFT_person_datetimeStart, DFT_person_datetimeEnd; -- Turn system versioning on ALTER TABLE dbo.Person SET ( SYSTEM_VERSIONING = ON ( HISTORY_TABLE = dbo.PersonHistory ) ); COMMIT TRANSACTION;
- 9. System generated temporal table SQL Server 2016 Temporal Tables9 30-Oct-17 Creating through SSMS
- 11. FOR predicate SQL Server 2016 Temporal Tables11 30-Oct-17 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
- 12. New clauses – AS OF DECLARE @datetime AS DATETIME2 = '20161108 20:00:00' SELECT * FROM dbo.Person FOR SYSTEM_TIME AS OF @datetime ORDER BY DateTimeStart ASC, DateTimeEnd ASC Clauses SYSTEM_TIME allow to realize temporal queries transparently for user and applications.
- 13. 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 New clauses – AS OF Returns a table with a rows containing the values that were actual (current) at the specified point in time in the past.
- 14. FOR SYSTEM_TIME FROM @Start TO @End Reference: http://sqlmag.com/sql-server/first-look-system-versioned-temporal-tables-part-2-querying-data-and-optimization-conside (Itzik Ben Gan) sysStart < @End sysEnd > @Start New clauses – AS OF 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.
- 15. FOR SYSTEM_TIME BETWEEN @Start AND @End Reference: http://sqlmag.com/sql-server/first-look-system-versioned-temporal-tables-part-2-querying-data-and-optimization-conside (Itzik Ben Gan) sysStart <= @End sysEnd > @Start New clauses – AS OF 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.
- 16. FOR SYSTEM_TIME CONTAINED IN (@Start,@End) Reference: http://sqlmag.com/sql-server/first-look-system-versioned-temporal-tables-part-2-querying-data-and-optimization-conside (Itzik Ben Gan) sysStart >= @Start sysEnd <= @End New clauses – AS OF 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.
- 17. 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.
- 18. More work, but much better … SQL Server 2016 Temporal Tables18 30-Oct-17 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];
- 19. 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.
- 20. Security for temporal tables SQL Server 2016 Temporal Tables20 30-Oct-17 • 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
- 21. Willfried Färber Principal Consultant Tel. +41 58 459 50 11 [email protected] 30.10.2017 SQL Server 2016 Temporal Tables21
- 22. Source code for the demos SQL Server 2016 Temporal Tables22 30.10.2017